yes, this is a great idea. There are several negative feedback scenarios which are outside the scope of review by the mods but which are unfair to the marked player. The most obvious are simple misunderstandings, poor sports, or an immature opponent with hurt feelings.
I, for one, like to play cardless games, and to be effective, these demand more negotiation, which in turn leaves me more vunerable to these scenarios.
The only drawback that I see to the idea as it has been presented is that a voting system simply favors those with more online friends. As an alternative, one might consider some variation on my "court of inquiry" idea, which would involve a volunteer impartial review -->
http://www.conquerclub.com/forum/viewtopic.php?t=30772