Very interesting topic!
Complaining that Game Chef doesn’t create more polished games is like complaining that NaNoWriMo doesn’t produce more award-winning fiction. Award-winning fiction isn’t the point of that, the point is to push people to make more stuff.
I think the fundamental issue is the fact that the critiques are open to everyone who designed a game. Design skills and critique skills often do not overlap. Critiques are as likely to be useful as from a random sampling of the population, more or less.
Which means a competition with a panel of skilled critiquers. That sounds very interesting! Problematic, of course, but it certainly could be done.