Again, I am not saying this is my preference, nor I am even advocating such a ticket. I'm just looking at a few things as I think Newt might do...
Romney does offer some geographic balance. Newt, as a Southerner, could potentially pick up some support in the upper midwest with Romney, who has roots in Michigan and Massachusetts. I am not saying he would automatically win either state, but it's possible. He could also help in Nevada, which I believe will in fact be an important state.
Style. Yes, this can help. Newt is bombastic, brassy, and brash. Romney is smooth and stays (usually) unruffled. Some would of course say slick or smarmy. He is also telegenic. Again, IMHO.
Business background. Newt has worked in academia and government. Romney's private-sector business experience could be an asset. Romney also has significant financial backing.
I also believe that Romney would come off well in a debate with Slow Joe Biden.
I am reminded of Reagan's gambit of asking Pennsylvania Sen. Richard Schweiker to be his running mate in '76. In Craig Shirley's excellent book "Reagan's Revolution", he gave the story of one Republican delegate in particular who, upon hearing of Reagan's selection, immediately decided to abandon Reagan. After thinking it over, he decided that "Vice-President Schweiker would be a lot easier to take than Secretary of State Kissinger" (speaking of Gerald Ford's SoS).
My own first ticket choice was Mitch Daniels/David Petraus (actually my first first choice was George Allen. Of course, that was afew years ago...) Again, I am just thinking of some possibilities.
Seriously, lay off promoting Mitt Romney, he does not belong in Republican party politics, and most certainly not on the Presidential ticket.