Hello there,
Yeah, the coolness system can be abused, but overall I don't think it does get abused a lot on the LD, I still get at least 70%~80% of the number of feedback I've given (from people that clearly seemed to have played my game), so the large majority of users won't abuse the system.
Comments with a direct link to the submission of the other person is indeed a good idea, it might lack that additional push though for being a little "abstract", people will likely just not play the other's game and the community will probably still get flooded with "play mine and I play yours" threads. But I think that it may be a good idea to see how the next game jams rating phase will be with this change, and if it doesn't change much, perhaps it may be a good option to try at least a variation of the coolness system.
You could, for example, make the user only receive the coolness points if he rates AND gives feedback on the entry, this would decrease the amount of abuse and it would also be encouraging people to give feedback on the other's game, which is the most important part imho.