This is either a weather balloon or a decoy:
Regardless of what McCain says, you aboslutely pick a running mate based on what he can bring to the campaign. No sense focusing on how he might perform as VP if you can't win.
So, this leak is either a way for the campaign to test the reaction among the base or it's a total decoy to give McCain room to vet his real top pick. Romney is a lightening rod and people love him or hate him...mostly they hate him. He strikes most people (and pundits) as an arrogant robot, but that didn't stop Dick Cheney from winning the second seat.
What does he add?
All in all, that doesn't look so great. Neither of those two boobs can outshine Obama's star power and the general vibe around Romney is that he's a faker, which doesn't help McCain much with those social conservatives who just don't trust him. I gotta think this is more of a decoy than anything else.