I think one of the things that holds people back in competitions is their lack of ability or time when it comes to creating media.
Maybe a competition that concentrated on user strengths would attract more entries?
So for a basic example a "Create a Mario style platfomer" comp would have 3 prizes. Best gameplay, best graphics and best audio.
That format sounds familiar, but the difference here is artists just create a spritesheet, no coding and likewise audio guys just produce music and sound fx, no code.
Coders write the game, but must use the same provided generic spritesheet and basic audio. That way the only differentiator between the entries is gameplay.
After the results are known, the winning audio and spritesheet designs are dropped into the best gameplay example and we have a quality collaborative effort that TGC can use to best show off AGK.