MI will be close as usual but I have not seen any evidence why it will swing towards the republicans this year. It was polling low for Obama due to him not campaigning in the state. I guess that may be changing. If I was Mccain I would focus on Pennsylvania before Michigan.
He still has time to pick and choose later... he's not going to be at serious cash disadvantage until after the conventions... I would wait a few months and see how the political situation, cash flow, and polls develop before ceding either state.