Personally I think the real value of the rep system was not in the little colored squares, but in the ability to leave a comment on someone's post without shitting up the thread in question. Just bring rep back but don't have the colored bars, that should pretty well eliminate any possibility of circle jerking. Instead you could just leave a count on the side of someone's post of how many times it's been +repped or -repped. Maybe even change the color of the post if it gets too far in one direction.