I think voting in general is broken. There is no way of stopping strategic up votes, or down votes. Obviously keeping it closed to jam members is a way of slowing it but it still wouldn't stop someone from having a few jam friends down vote a game they think is going to win or up vote each others games with 5 starts. Maybe if itch had something in place that if you voted 1-2 star your would have to leave a response but even this would have to be moderated by the jam admins, and they are not making anything from this. That is alot of work.
You could also stop having any prizes which would rid of more schemes. That would really suck though. I was stoked when i seen i could win something if i made a dope game.
Honestly you guys tried to do something that works and that is awesome. I like that not only is it community votes but also a judging system.