I don't think that's a bad idea, and since they are GPL (as was the requirement for the contest) techincally anyone CAN fix them. As you say will they? Or a better question is how to go about it.
A list with reported broken themes is a good start. Of course then maybe the person who makes the fix wants a credit, and then the author says no way man I designed, and then all your chickens cry out in digust or something.
At the end of the day, they're GPL so it's anyones to fix - how do you go about managing this? Perhaps you use the theme repository or create some list which states which themes are broken, who fixed and what the fix was in the codex?
It's a pretty complciated thing, seeing as there are 139 themes, and let's say around 20% are broken pretty badly, 40% require minor fixes, and the reaminder and generally OK unless someone finds something really odd.
In addition, is it broken if the theme is not designed for a specified function? IF it's not designed for the use of, I dunno, quicktags within comment or gravatars or something of that ilk because of its structure.
I don't think you can offend anyone really Podz, I mean at the end of the day, a working theme is to the credit of the designer, not to their detriment. Otherwise users would simply avoid the theme, and possibly the author altogether, so it's for their benefit as well as improving distribution for a theme that might be broke, but otherwise sound and just waiting to be fixed.
@ Root 8/10 the response is usually a solution, the 2/10 is contact the author and they tend to be fairly simple problems. As it is most theme support ends up at WP rather than the auhors, because it's the support site and that's what rings peoples heads.