...probably many of you have already been thinking along these lines:
1) As we all know, we'll get a better deal when the new House takes over and Pelosi is sidelined as the squalking nothing she really is, and at the cost of only a short period of pain, but even more importantly;
2) As long as the expiring tax rates aren't dealt with, Senate Republicans can just point to that 42-member letter and say "no votes on anything else--or are you really going to go out into the media and try to make a case that the DREAM Act (amnesty) and DADT (corrosive to our military cohesiveness) are more important than dealing with the tax situation? Go ahead, make our next 2 years."
This way, Republicans have an excuse to filibuster, without having to argue the issues on substance; which, I'll grant, opponents are in the right in, of course, but far better to be able to say "you didn't deal with something so important as tax rates for all Americans, you punted on this for 2 f'ing years, and you expect us to do anything about this shit?! (DREAM and DADT)"
The tax battle is far more valuable as a roadblock to the regressives' cram-it-down-our-throats-in-the-lame-duck agenda than as an issue unto itself.
Also, if this goes to the House and passes amended, Republicans are falling into a trap. Then they'll be cast as the abd guys if they filibuster on the grounds that the deal was broken.