re: Then again.....
I think one party change per political career is about all credibility can stand. Besides, there is no constitutional reason a running mate from an opposing party couldn't run. In fact, I think it would be a very positive development, and it would totally baffle your opponent. Remeber Jimmy Smits picking Alan Alda in that White House TV melodrama whose name escapes me now?
What I have noticed is that over the years candidates often pick as running mates people who are chosen only because they will appeal to certain voters (or at least, not alienate any groups). Those of us who aren't close followers of the Washington scene usually react with a "Who IS that guy?"