So I'm just thinking off the top of my head here ... wait, that can't possibly be the right metaphor.
ANYWAY, I had a crazy idea. What if we did a challenge every single day? Like the Pop Quizzes, you'd only be able to enter each contest once. I could reinstitute the "thumbs up" functionality, and instead of a winner or a "Jeff's favorite", it's just a way for everyone to participate and get their work out there.
Reddit has a "Daily Sketch" challenge that works like this. Take a look and see what you think, and please share your thoughts in the comments below.