I do not think that you are an island at all. Ancient eras and modern ones feel almost like different games. Your relation with the territory is completely different. There is room for all. The thrill of Civ is contributing to forge history and see things from different perspectives as time passes. When someone wants to dwell on a particular age, it is possible to do so as well, via starting options, scenarios and mods.

100%. I'm only on my second full game of Civ IV, but I'm slowly getting acquainted with the modern era and how to play it. One of the things I love about the game is the variety of ways to win. Unfortunately, and maybe due to the small sample size, I'm beginning to see a pattern -- the most realistic way of winning is through domination or conquering.
- Culture seems extremely difficult.
- Diplomatic seems do-able but is very time-consuming and makes you play deep into the game (which isn't necessarily a bad thing).
- Space race is something I personally have little interest in trying so I have no take on it; though it seems you're forced to play into the 21st century.
- That leaves domination and conquering, which of course involves war. I like playing with continents so that forces you to have a navy, which makes attacking enemies on other continents and/or islands a very time-consuming task (which I'm dealing with in my current game). Also, I forget if you're able to adjust the %s for Domination victory. I know you're able to in Civ III. That would make that type of victory a smidge less daunting.

Culture victory is high-risk/high-reward. While it leaves you very vulnerable, it can win much earlier than other victory conditions. You need to be playing close attention to this one on the victory page and watch if any of the AI's are getting close to it, because once they get a cultural engine going the last few thousand points of culture come really quickly. The thing with culture victory is that you basically need to go all-in on it, setting up three cities with massive culture output then cutting tech output to zero in the early renaissance to go all-in on culture. This means you will fall drastically behind in terms of economy and technology. If you don't get attacked, however, this is basically a free win.

Diplomatic victory is extremely arbitrary and comes down to the whims of the AI and whether they're willing to award victory to someone. The Apostolic Palace is also very inconsistent; you need to get one city with a chosen religion in every empire, which can happen really early on pangaea where Buddhism and Hinduism have spanned the globe three or four times before the AP is even built, or never on archipelago where you can get someone like Isabella or Saladin off in the corner with Theocracy who will never let a different religion into their borders.

What really bugs me is that there's very little in the way to gauge this. You can't tell how much support an AI has for victory until a vote is held, which might just be the end of the game. Even if you do know they have a lot of support there's not a lot you can do about it since relationships with different empires are often mutually exclusive (start being buddy-buddy with Asoka and Wang Kon will hates your guts for it) and this makes it very hard for the player to build large coalitions. The AI doesn't play by the same diplomatic rules as the player does, and they can often make large coalitions as a result.

This is the only victory type I keep disabled. I find it annoying since I like the AP and UN mechanics other than the victory vote, and dislike how their other feature are completely disabled just because I want the victory condition removed.

Space race is a very uncommon victory type on standard settings. Going from the Ancient era to the Future era gives a lot of time for other victory conditions to happen. Most of the time when it happens, the empire that triggers it was so far ahead technologically that they would have won by other means anyways. If you are playing with a modern era start, though, you need to pay close attention to this one since it can happen very quickly. The other place where it can happen frequently is on continent games with a very large number of continents. With 5+ continents Domination becomes an impractical victory type and if you're the economic front-runner just rushing for space race is often your fastest win-con.

Winning domination is pretty straightforward on a 2-continent game. You want to have your own continent completely conquered by the early renaissance so that you're free to do a full eco-boom before making contact with the other continents. Identify the weakest independent empire on the other continent and use them as your invasion point to establish a foothold, start ferrying over troops, and once you have enough you can start your conquest/vassalization of the second continent. 3 continents isn't much different since you can usually win with just two continents and can ignore the third. It's only at 4 continents or more that Domination starts become a real challenge since it's very time-consuming to set up that beach-head and ferry over a large army, and doing that for multiple continents takes too long. Every additional continent just makes Domination less likely.

Interestingly, this does not apply to the extreme case of archipelago. The key difference in that case is that the defending empire is also split across multiple land masses (whereas on continents only the inter-continental invader needs to transport units while the defenders can reinforce just fine even if they've completely lost the water). This allows you to block reinforcements if you have naval supremacy, and means you need to commit much less to winning a beachhead on an individual land mass. While it can still be a logistical nightmare, come the modern age a force of marines, destroyers, and aircraft carriers can make very short work of small land masses with 1-3 cities (and, although it's a bit slower, a big stack of riflemen and cannons will do the job just fine too).

go watch some pvp games and see how the winners won

It's achievable, but it's not a victory condition you can decide to pursue when you're already late game. Some preparation is needed. Early-mid game you want to settle at least 9 cities so you can build cathedral-tier buildings (cathedrals, mosques, synagogues, stupas, etx.) in your legendary cities (each cathedral requires 3 temples, hence 3 × 3 = 9). You also want to fish as many religions as possible, either by founding them or by opening borders with other civs. For each religion, you put its cathedral on the cities you want to become legendary. Cathedrals are the most effective culture multiplier buildings in the game (+50%).

With Radio you get access to another multiplier (broadcast tower). The Modern cultural wonders (Hollywood, Broadway, Rock & Roll) are also modifiers, but not as cost effective. Wonders won't increase significantly your culture unless they are buily very early. They generate great people points though.

Meanwhile, you need to develop your cities. You want your three cultural cities to work as many cottages as possible and grow them to towns. When you reach a technological level you're comfortable with (Music for cathedrals, Radio, Mass Media, Corporations or perhaps Rifling if you feel threatened), stop researching and crank the cultural slider up.

Another option is to go with specialists (with enough food and Caste system you can run as many artists as you want). Save your great artists and uae them late-game to even your cities' culture with great works (culture bombs).

Corporations can also do very fun stuff with extra resources and generate a lot of culture, but they come relatively late in the game for a cultural victory.

One of your cities should be producing military units (almost) non-stop, so you don't become a juicy target for warmongers. Choose a high production city.

I'd say that waiting for Radio or Mass Media to crank up the culture slider is waiting much too long. Culture victory should be aiming to win before anyone hits the modern era anyways. Rifling makes sense for self-defense, but you really don't need any tech after that since the combination of cavalry and riflemen is generally enough to keep you alive into the industrial age. Aside from wonders (which don't really make sense for culture victory after the medieval period; just build culture directly instead) there is nothing on the tech tree between Liberalism/Music and Mass Media that helps with culture.

Yup; absolutely a great way to produce huge amounts of culture.

Unless you're playing a very small map, you need to be absolutely enormous to have enough resources to get good culture out of corporations. And culture victory generally keeps to a compact size so they won't have enough resources to pursue corporations. Creative Constructions is probably not worth founding, you're better off just spending the great engineer to rush a wonder in the classical or medieval age rather than saving him for later. If you are in a position to run it Sid's Sushi is quite good, but it also comes very late so it's dubious to tech towards it.

Great stuff Darwin; a lot of good info. Much appreciated.
It's funny because Isabella and Saladin have each been in both of my games and have been a pain. I'm currently aiming for a Domination win. My map has basically 3 continents -- one small that has multiple island clusters, one medium, and one large. 4 civs, including myself, started on the large one. I became close friends with Kublai Kai early who helped with a few wars. I eliminated Saladin after I decided, somewhat late, to go for a Domination win. I pretty much own all of the small island cluster continent -- Spain has a small city that doesn't do much. Finally, Germany owns all of the medium-sized continent. Their military, oddly, is small and I'm currently in the process of wiping them out. Hopefully that puts me over the top. Transporting troops over was time consuming in the beginning but the process went a lot smoother once I got the hang of proper routing and troop building.

Your points make total sense and would seem to be very effective. For me, I don't see myself being able to commit to Culture victory from, essentially, turn 1. To my detriment, I'm not one who can fully commit to city specialization (regardless of what type of victory the goal is). No matter what I do, I always tend to try and built up some amount of religion/culture, commerce, and military in every city. Even if it's only only one building. In the long run I might be wasting turns, but I can't help myself. I like to strive to have every city be useful in multiple ways.
This is also only my second game of Civ IV so that ideology could easily change. For example, going into the game I really liked the variety of ways you could win. But I've already somewhat given up on ever trying to win via Space Race or Culture (though I love having culture in my cities, regardless of circumstances).