The rest of your argument is just wishful thinking.  Party discipline on both sides currently is stronger than I've seen in a while and the country is pretty well divided on many fronts.  The moderates you identify in both parties (plus libertarians -- who've never had much impact on the politics of this country anyway, etc.) don't appear to be coalescing into one big "middle".

I see no real world support for your argument other than the current poll numbers for the Pres -- but I don't think he's falling in the polls because people are waking up or moving to the "middle."  Iraq's going bad and gas is skyrocketing.  If either or both of those go the other way, he'll be back in favor -- with approx 50% of the people.  The other 50% (me and the other smart ones) will hate him regardless of the turn of events.