I dunno, I think a Guitar Hero tournament sounds pretty lame. Not only would there be no need for any sort of tournament mechanics (as it'd just be a "everybody post your scores, see who's highest"), there'd be absolutely no interaction between players.
I've always believed that, to have a proper multiplayer experience (especially in a tournament setting), the players would have to be directly against each other in such a way that one's actions affect the other player's situation. If you're racing, it'd better be on the same track at the same time, and there'd better be ways to make it "interesting" for the other guy.
Otherwise... you're just comparing numbers.