Yes!!
Im adding this now to the features wishlist.

I'm absolutely not suggesting the downloader be mandated. more what I'm proposing is that it become an optional front-end for the service. If a game you own is updated, or a new version of DOSBox is released, the downloader could detect and update that for you.
I used Steam as an example, because it's the only other program I can think of that does anything similar at all. I'm certainly not suggesting it as any kind of idea of perfection. I CERTAINLY don't want any Steam-like DRM schemes added to anything on GOG.
I love the service as is, but I was thinking this would bring more unity to customers' game collections.

Seconded
I don't want the downloader to turn into Steam too, but I'd like the Downloader to have some of Steam's functions, such as a friends list, the overlay, a community website etc. In-built browser would be nice, but I wouldn't call it mandatory like the previous features
But then this would require more effort than what it's worth. Heck tbh I'd rather GOG focus on giving us better GOGs and more features on GOG itself first (3D virtual shelf? <333333)

I think the downloaders point is simply being a downloader, so I don't think theres a need to add things like friendslist or update thing for dosbox and the like, though I do think if a game gets patched it would be nice to be able to download the update alone with the downloader (or browser).
I personally have only used the downloader once and I didn't really check all the diffrent settings and the like, but things like shutting down when download is finished should really be added.

That matters for users. *nods sarcastically*

I think the Shut down after the download is completed idea is the only thing that needs to be added. The downloader is what it says it is, and should never turn into bloatware.
Then again I'm sure some people think AIR is so full of bloat its got into orbit.

it'd be neat if the downloads were peer 2 peer.

That's a bit like BitTorrent. No, not that BitTorrent, the one where they expect you to pay $9.99 for a game and you also have to host the file and seed it to others.

The only reason for that (as I see it) would be for increased download speeds, but I'm quite happy with the speeds I'm getting from GOG (or rather bitgravity, where the files are hosted). I usually get about 2,5 Mbyte/s per file when downloading 3 or less files at once.

I get fairly good speeds as well, but having a peer 2 peer option gives GOG a nice gray area scapegoat.
"oh, you speeds aren't working well? I guess it's the torrent."