Would I visit a theme indexing site? If it earns my confidence by reviewing the themes (both initially and after updates - especially if the theme changes ownership), publishing their review standards, and providing us reason to believe that they are not favoring a particular theme shop or otherwise showing bias, then yes. Of course, the use of affiliate links could be construed as bias, but reviews - and just finding the themes - takes time and commitment, so money does have to come from somewhere.

Basically, if I can be assured that I (and, more importantly, novice users) will get better results than a "free WordPress themes" Google search, then it's already worth something. But I do tend to take any index with a grain of salt and wonder where the loyalties lie.