If you haven't already read Jonathan Cohn's terrific piece about McCain v. Romney in Michigan, you really should go do that.
One thing that struck me while reading it was that the race could, in some vague, indirect way, provide insight into the Hillary-Obama matchup. For example, Jonathan writes:
McCain is running on the same themes that have gotten him this far, not just in this presidential campaign but over his entire career: integrity, character, and leadership. And, when voters are less worried about their livelihoods than they are with the culture of Washington, those are terrific themes. But Michigan has the nation's highest unemployment rate and slowest growth. It's also losing residents faster than any other state. The folks here like straight talk, but, it seems, they like Romney's promises of new jobs even more. In the Free Press poll, Romney led McCain by nearly two-to-one among people who considered the economy their top concern.
Granted, there are all sorts of differences between the McCain-Romney race and Obama-Hillary. Among other things, Obama is a much better speaker, but also much less experienced, than McCain, while Hillary doesn't have to deal with the "phony" label Romney's acquired. Also, Republican voters tend to look for different qualities in a president than Democratic voters do. Still, on some level, the Democratic race offers a similar choice: a candidate running a less tangible, more thematic campaign, and a wonkier candidate trying to appeal to voters with a specific laundry-list and an argument about competence.
If McCain's message sells even in recession-ravaged Michigan, I think Obama can take a measure of encouragement from that. (Though only a measure--in addition to all the other caveats, the race is funky since it's open to Democrats and Independents and there's no race on the Democratic side.) And if Romney does exceptionally well today, then it could foreshadow the rising importance of economic self-interest. (Though obviously most other states aren't in the kind of shape Michigan is.)
I have a feeling Jonathan was thinking something similar when he wrote the piece, since we've been batting this stuff around internally over the last week or so...