bwh2, you made some good points, and I agree that the Suns and Cavs would be average without their stars, but the thing that Billups does NOT do for his team, is make his teammates better. He does make his team as a whole better, but he does not actually improve his teammate’s performance. Nash has been the best at doing this–he has given many no-name players a turning point in their career. So the Suns success with Nash, while he is the biggest part of it, is not solely caused by him, but rather his teammates benifiting from him.
Kobe’s case is kinda like Chauncey’s, where their teams may have a better record because of the player, but it is only because of his individual performance. To me, the MVP should go to the player who makes the biggest impact on his teammates, and I think that is what you said as well.