Just to let you lot know what I'm up to at the moment. I recently got the urge to work on high-res versions of the IdBase textures. The idea was to make something that looks almost identical to the originals at a distance, but shows the added detail up close.
I know there are existing attempts to retexture quake, but they are generally of a much greater scope. Here's an in-progress comparison:
http://www.planetquake.com/starbuck/retex/