I say scrap the party concept and go back to the beginning, where people voted on the individual, and the runner up would become VP.
President Bush and Vice-President Kerry? President Reagan and Vice-President Mondale? and my favorite...President Nixon and Vice-President McGovern.
Your idea would certainly make the U.S. government more interesting.
You bet it would. Of course, if that system was in place back then, who knows what the combination would have been. You could still have ended up with Reagan/Bush because Bush out performed Mondale in the polls, etc.