I say yes. The class 1 Senators are already 18-15 Democratic. Gaining 5 seats would make that be a lopsided 23-10 Democratic, even though the Republicans would still control the Senate.
Class 2, which will be up in 2008, has far more pickup possibilities for the Democrats, seeing as it's 21-12 Republican. Just evening that up would give us 4-5 seats, while we're already ahead in Class 1.
Also, taking the Presidency makes 1 less Senate seat be needed.
But Class I is a lot more Dem-friendly than Class II, looking at the states included.