I think this also speaks against balancing the ticket as an electoral strategy. In the old days, when vice presidential selection might have been part of a deal involving both halves of the ticket, balancing was a nomination strategy, not a general election strategy (although it could have been the latter, too). But nowadays, of course, there's no need to lock up the nomination through Veepstakes, although certainly keeping the party happy is part of what nominees must consider.
At any rate: what would Mitt Romney need to do to balance the ticket, anyway? Not location; Romney goes the president one better, with at least three home states (Michigan, Massachusetts, and while it's a stretch, Utah) to the president's two (Hawaii, Illinois, insert Kenya joke here). Religion, probably; a ticket-balancing Romney would presumably go with a Protestant. Ideology? Yeah, the only moderate taken in the last forty years was George H.W. Bush thirty years ago; that's not really going to change, although given the state of the current GOP most people who are not disqualified because of a long sheet of totally wacko statements run the risk of being considered moderates.
Beyond that, Mitt Romney is an unusual combination of being old and inexperienced (with only four years in government, Romney is even more inexperienced than Barack Obama was in 2008, despite being far older). That's not an easy one to balance!
In particular, with his only experience at the state level Romney has the typical governor's lack of foreign policy and national security experience. His business background basically is more of the same: the economy, not foreign policy. Usually, governors go for someone who can balance that: Ronald Reagan picked UN Ambassador George H.W. Bush, Bill Clinton picked a senator who boasted expertise on military matters, George W. Bush picked a former Secretary of Defense. The only rumored candidate who really fits that is Rob Portman, who spent a year as US Trade Representative and has a a year and a half as a senator, although that's not exactly impressive.
Again: I don't think balancing as a general election strategy makes much sense, anyway. But if he's trying to do that, he should basically be looking for a post-boomer Protestant with lots of experience, particularly in foreign affairs and national security. Good luck finding that.