Here's the thing.
I believe Obama is going to win the election. It'll be closer than 2008, but I don't think it's going to be particularly close. Even if we allow for the possibility of extensive vote suppression–as an aside I think it'd be an excellent idea if the Divine Nine added voter registration and protection to their list of mandated programs–the Republican Party isn't going to be able to suppress enough votes to win swing states like Pennsylvania. It isn't going to happen.
Given this, why do the debates matter?
I'd argue they matter not so much because of the (ignorant) "independent voter". They matter because they represent the best chance Obama has to rhetorically destroy the various ideas the Republican Party has been passing off as sound policy. This isn't a battle against Mitt Romney. It's a battle against the GOP. Beating Romney decisively in the election won't mean a thing if he doesn't take advantage of that victory to embed a new set of ideas about how to govern. He should hang the GOP's attempt to suppress votes, to hijack the economy, to radically redistribute wealth upwards, around Romney's neck like an albatross.
I doubt this will happen, because the Democratic Party is beholden to Wall Street as well.
But this is what SHOULD happen.