But let's look at the candidates: One moderate running this year is Ganske (RINO-Iowa). I still hope he beats Harkin (anyone's better than him) but he won't. Norm Coleman (MN) is more on the moderate-conservative end, based on his record--but not a RINO, and I think he'll win. As for Dole and Alexander--she's posturing to the right, and will probably vote to the right as well, but not because of any innate beliefs she has. She'll be an 85 on the ACU ranking, is my prediction. Lamar is "sort of" moderate, but he's actually, in my opinion, more conservative than Fred Thompson, so no loss there--and we could even get Ed Bryant, though I doubt it. Cornyn is a conservative. Forrester (NJ) is a RINO, but at least he's good on immigration. Chambliss (Ga.) has a good record in the House, as does Thune (SD), as does Sununu (NH) (although it's a shame to see Bob Smith go).
So all in all, you're losing two conservatives and one moderate in retirement, and getting one conservative and two moderates to replace them.
You also have a conservative replacing a conservative through the primary (NH).
Then you have three conservatives trying to replace Democrats (two will succeed), and two moderates trying to replace democrats (NJ and IA, both will fail). So if you want me guesstimate, I think we'll have a net gain of conservatives, especially if Hutchinson hangs on in Arkansas--which he will.