I'm happy to having found a post like this in the middle of the R4R storm.
I share most of what you said, but I'm not very convinced about the solutions.
Premise: this is my first game jam so my opinion may not be the most comprehensive one!
I think that what is missing here is that a game jam doesn't end when you submit a game and you are not really helping someone by simply saying "nice game" or stuff like that. Unfortunately there isn't much real human interaction and what makes it worse is that those who have the most rates have the least need to do that, but they are missing the best part! Personally I have played all the games of the people who have commented mine and I look for games alternately filtering between Most Karma, Least Rated and Random but choosing who actually participates in the game jam (comments are very indicative for that).
In a real-life context, you play my game, I play yours, and then a dialogue begins. That's how it should work online too.
I don't know how such a result can be achieved, perhaps simply through people having a greater desire to learn and less desire to stand out.