You know, by doing things like allowing for higher resolutions (obviously the textures would look the same as the game's original maximum resolution, but you'd see more) or including community-made bug fixes? Anything like that?

Not usually, although there are two games that were supposed to be a special edition like that.

I know for the Might and Magic 6-pack there is a stickied link to a fan-made update in the forums, but it isn't applied by default.

All GOG does is patch the games with the most current official patch, remove or disable any DRM and ensure that the game will work on a modern Windows OS. Beyond that, the games work, look and feel exactly as they did when they were originally released.

If you're looking for a widescreen/high resolution solution you might want to check Widescreen Gaming Forum and/or the forum itself. If there is a way to change the resolution, you should be able to find it in one of those two places.

This is certainly almost always the case, but doesn't Master of Orion II come with the unofficial fan patch installed? GOG did not develop the patch themselves, but I guess it's an improvement.

Gabriel Knight II does indeed come with the fan patch pre-installed. It's probably safe to say that fan patches aren't included unless they're essential to getting games running.

Hey, GOG managed to get I-War working in current OS installations (which was sort of a miracle to start with). That counts as "improving" to me.

GoG recently updated Betrayl at Krondor with its sequel and I'm sure the update is free to those whom have already purchased it.

I'm only into optional graphical updates (MODs for instance) as part of the reason I purchase these old games is that they can run smoothly on my old computer.

Well, all DOS games come with build-in and already tweaked DOSbox emulator, so they run smoothly in fullscreen, resolution as high as possible. I think it's important, so you don't have to install and tweak dosbox yourself.

As you may know DOS games can run properly only in Windows 98 or older versions. If you try to run a DOS game in newer Windows, like XP, it'll be extremely laggy and you'll never get sound or music to work.

Arx Fatalis has a special gog patch but I think that's made by the developers.

They aren't special editions which seems to be what you mean... they are classics as they originally existed, only modified if it's needed to run them.

It would be nice with a few fanpatches preinstalled with Interstate '76, since, as far as I've been able to make out, it's still not running smoothly after gog.com's normal fixing...

They do sometimes fix gameplay issues in games. I know they did with Outcast. But typically it's just a question of them patching it up, making sure they've got it working in XP & Vista (now 7 too), then releasing it. I don't know if they've ever increased the available resolution options themselves. Mostly they try to leave the game as it was intended.