It depends on how mature your development environment is.
When I worked at Gremlin Graphics I was sat in a meeting and we were discussing new projects. Ian was talking about doing a snooker game and some of the guys thought it would be too difficult to do in 3D (this was in the days of the Atari ST and Commodore Amiga). While in the meeting I coded up a snooker table with all the balls and a little bit of physics.
Okay the balls were really planets from FOFT, and the physics assumed the spheres were actually cubes, but it took me 10 minutes
Sometimes a contest like this can be used as a test bed for ideas. Okay you are not going to be able to write stunning new special effects and commision new music, or get megabytes of new graphics done, but you can test game play.
I think game play is one of the things that we have lost in modern times, the focus has gone into graphic display code and making things look stunning rather than finding new fun things to do.
A short time span game contest SHOULD focus the mind on game play rather than 1024 lights, real time shadowing, megatextures, particle effects, etc. etc. etc.
Note the SHOULD