I didn't think of the "12 times the work" aspect...
...and I have enough trouble trying to get my own games read, let alone reading through the work of others.
I could probably pull off a seasonal thing...best winter game, best spring, best summer, best autumn...giving them "Silver Bananas" and entry into the "Golden Banana".
Otherwise, it might be worthwhile splitting up the contest into sub-categories such as "Layout", "Artwork", "Innovation", "Best Overall".
Just throwing ideas around....seeing what sticks.