Chris,
You're exactly right on this, especially if you want to build a progressive majority. This seat and Foley's seat are anomalies this year that are amusing, but even in other uber-red seats, Dems are only going to hold the seat with Conservative and centrist candidates.
If you want a progressive Congress, the seats that are more important are the ones where progressives can win, not just Democrats. Not to understate the importance of supporting conservative Democrats to get the neocon hate and killing machine out of power for good, but guys like Ellsworth, Shuler, Lucas, & Trauner in the House and Tester and Webb in the Senate aren't going to do progressives any favors if they're elected.
Winning the PA and NY and CT and MN seats are the seats that will advance the progressive movement much more than winning in WY or ID.