I just thought of one advantage to McCain. As a Republican (even in name only), his funding comes from the RNC, thus, we have more power to hurt him in the pocketbook. We can have more influence against bad legislation via our donations. If he supports bad legislation, we can shift our donations to PACs that support our cause. If he makes good choices, we can reward with donations.
We don't have that leverage with Osama, er, I mean Obama.