I don't think it matters who wins. Barring a major calamity (terrorist attack, etc) I see us muddling along pretty much like we have already. Obama has probably already passed all the major legislation he will during his first term. (Given the scope of the health care bill, that's not necessarily to say he won't have accomplished much.)
I do think that people have over-estimated the impact of the Tea Partiers. Those who love the Tea Partiers really love them, but you don't get more than one vote just because you are intense about it.
I think a lot of people, particularly women and minorities, hear these far right wing candidates and don't say or do much, but quietly cringe inside. And vote accordingly.
McCain wasn't a classic Tea Party candidate, and he won the Republican nomination. Obama was a Tea Party nightmare, and he won the presidency.
The proven path to winning in politics is to be on the fringe in the primaries and rush to the middle in the general election. The Tea Party strategy is to be on the fringe and stay there. If I'm wrong and they do really succeed, it's going to signal a whole new politics.