Your post is right on, Bill.
But I think it's ever worse than that.

Once the big multinational corporations complete the takeover our government agencies, the courts, the media (including those "internets" when "net neutrality" legislation is defeated), our financial institutions, and the mechanics of our voter registration, voting systems and vote counting, the control may well be so complete that no Democrats, liberals, populists, or even true "moderates" will ever be elected again in sufficient numbers to have real impact on our laws and policies.

We're pretty close to being there, with such well-funded right-wing control of radio stations, TV channels (including local news), and even the internet (by way of those well-paid Republican shills who constantly edit Wikipedia to rewrite history and who flood message boards and talk shows with deceptive calls to spread the right-wing talking points).    The Democrats had some chance to change things, such as breaking up the media monopolies or pushing for real campaign funding reform, at least on the publicly owned airways, but they didn't really try very hard.
If the Democrats retain control of the Senate, they can amend the Filibuster rules to prevent most of the obstructionism the Republicans in this past Congress have engaged in. If they retain control of the House, they can continue pushing for legislation that will benefit the general populace instead of the tiny minority of the uber-wealthy.    But if the Republicans take control of either house, all the Democrats can hope to do is maybe slow down some of the reactionary legislative agenda of the Republicans.

Oh, and one other thing:
It's fairly likely that many of the big corporations are deliberately holding off on spending their $ in ways that would boost the economy, job creation, etc. - either because they want to make Republican victories more likely this year and in 2012 or maybe just because they're risk-averse at the moment and are hoarding cash. That's likely to change next year or at least by early 2013, in which case the Republicans, if they're in office, will eagerly claim credit, and the media will buy into that.