Agreed, and I kinda think Social Security is key here. The point wasn't just to fend off privatization. The point was, or should have been, to so totally discredit the idea that you can use it as a campaign issue, where you continually remind people that these are the guys that wanted to take away your SS benefits. That's what the GOP would do if it were the other way around. The Dems did the first part really well, but it means little without the second. And it has the equally important benefit of establishing for the next 10 years that anyone who fucks with SS is going to pay a political price. If they don't exploit the whole sorry episode for every ounce of political advantage, they'll just have to fight the same battle again in 5 years, and ultimately they'll lose when someone comes along who's smarter about it than Bush was.
Also I wouldn't get too optimistic about taking back the Senate. They'd need to pick up 7 seats and there just aren't 7 vulnerable GOP incumbents facing re-election. Still, a couple in the Senate and a bunch in the House would be nice.