Good analysis. I'd expand it be adding another flavor of center: Ticked-off Centrists. People who register their dissatisfaction with the choices offered up by the Parties by refusing to choose the lesser evil.
The AU statistics report that Democrats increased their share from 16.8 to 17.9%, while Republican share "declined sharply" from 19.2 to 16.8%. One explanation would credit 1.1% of the Democratic gain to former Republicans who switched sides; but maybe it was a case of Republicans who chose to sit out the election, while the issues motivated more people to get up off the sidelines and vote Democratic. Turnout increased overall 0.7% but I can't say where they came from.
There's a commentary from the Center's director which will, of course, strike Republicans as a bit partisan. But even subtracting that, it describes what I think probably happened:
Republican Repudiation: Democratic Opportunity: The 2006 election was a total repudiation of the Karl Rove/Dick Cheney version of conservatism. Without Bill Clinton and John Kerry to play off against and without a very proximate backdrop of September 11, the Rove/social rightist version of the Republican Party was defeated every where but where the social rightists thrive – the Bible Belt – the South and particularly the Deep South. (It should be noted that Virginia has a Democratic governor, a Democratic U.S. Senator and a Republican Senator of a vastly different stripe than the GOP tigers in the White House and Capitol Hill.
Leaving aside his disapproval, he's describing a mechanism of rejection or repudiation. The GOP lost support, and it'd be simplistic, I think, to assume that those people simply switched sides.
I can't say I find the Apathetic Center to be extremely alarming. Regrettable and deplorable, perhaps, but there's ample precedent for people giving over their votes to proxies, e.g. corporate shareholders. Those who choose not to vote are choosing to let us decide for them. You can't not vote, you can only choose between active and passive voting.
The pendulum analogy is a hoary one, true, but not without its uses. We can apply some friction as it whizzes briefly through the center, so that its farther extreme is not so extreme, and once again as it comes back. Over time we can try to reduce its excursions to make it spend more time orbiting the center. That was the metaphorical logic behind my suggestion that we non-Rightists resist the temptation to give the pendulum another push by gloating and trying too hard to capitalize on our victory.
The pendulum analogy would also suggest that we'd have maximum influence on it when it pauses at the extreme of its arc, but I don't see much practical value in that. We'd have to stand out there at the extremes, and I'd rather not, thank you very much.
Growth at the center would come from a number of sources. Motivating the apathetic could be a significant source, with the caveat that we're drawing upon a population that probably has a rather shallow grasp of the issues. Drawing upon the disaffected or cynical may have more power, because the message that an invigorated center stands in opposition to the partisans is likely to resonate with people who've rejected the partisanship. A third major source of centrists will be those who are naturally centrist, but felt compelled to take sides, perhaps out of a sense that their vote wouldn't count if they didn't.
All of them need to be reminded, or convinced, that the center is the historical and natural source of power in American politics. That's a message that I would hammer out day and night.
I wouldn't advocate growing the center using a third party. That contradicts the principle that the center's power derives from its independence. An organization would be helpful, but it would have to be carefully nonpolitical, by which paradox I mean that its focus would be properly on "metapolitics", shining a light on the mechanisms of politics and power and rhetoric, and giving people the intellectual tools to maintain their own independence.
A utopian dream, in other words?