I think your idea of "popularity" is a little too simple. No matter what categories a jam host gives, the popular voting on a major jam WILL be a popularity contest, but not based on raw number of votes. The winners will be who ever has the most enthusiastic players.
This is why I try to say something concrete and negative about any game I play regardless of whether I enjoyed it. In the absence of an actual monetary prize (which jams occasionally will have), the actual most worthwhile part will be what the participants learned. Yes, that includes whatever amount of exposure the host promises. Further, the majority of participants will have more need to learn what they're doing wrong than what they're doing right, because whatever they did right is ingrained enough to do under pressure.