Motivation to beat the teams from the other conference? Isn't that what the All-Star-Game is for? Not to mention the fact that homecourt-advantage should also be a very relevant factor. What more motivation do you need?
I think it will be tough enough for the "minor" teams to catch up, even if we don't come up with new hand-outs for the already dominating teams.
I also think this would be an economic incentive so randomly distributed, that it might as well have been distributed ...completely at random.
I like the idea of bringing a bit of thrashtalk, the game within the game. Each division have their own forum, bring your best heckler-moves and provoke the opposition to go all Crunch-Time and ballistic in a game they were bound to lose anyway, fire it up!
I also think that as teams settle more in the different divisions, the rivalry between the conferences will build by itself. Sadly, the top level in each country is the only place you'll ever get to defend a championship...