Several other points, here.  Even moderate Republicans have been fearful of offending Bush. Take Pennsylvania where Arlen Spector successfully (and barely) beat off a right wing challenge.  Spector, perhaps as payback for Bush's support in the primary, as gone along on some questionable legal/judicial maneuverings he would probably have challenged in the past.  He may be the most Progressive Republican in either chamber (rating from Progressive Punch) but he is no Lincoln Chafee by a long shot.

Second, the number of Republican moderates who have retired after successfully beating back Club for Growth challenges is meaningful.  Some, like Marge Roukema in New Jersey, have been succeeded by their righty challengers.  Others. like Sherwood Boehlert in New York, have been succeeded by Democrats.

Third, in cases where unpopular righties risk otherwise safe seats they have won some primaries (see Jean Schmidt).  Only extremists like Schmidt, Garrett, Cubin, or Musgrave could lose their districts.

We shall see but I think it bodes well for Democrats in the short to mid range.