You know what we could do, there was that one guy on the chat the other day posting pics from his Interlopers map battle...
They were given a basic template (like, in their case it was a bridge) and then had to build a map (or a section of a map) around that...
Why not as a small thing do like monthly or bi-monthly mini-map "battles" ... someone comes up with a template (like a bridge) and you have to create a 2048x2048 point, or spawn room, or something, tf2 related. I mean, most of us in a weekend could come with something decent enough. This might be a good way for people who are inbetween maps, or don't have time for full maps, to practice their skills, get feedback on their skills, or just as a way to prevent people from getting rusty...
Thats just me though, I thought the map battle idea was interesting... (and epic sounding). Don't know about prizes for winning, maybe something forum side like "Battle won" on their profile page or something...