How many of those republicans are retiring because they know they will lose the next primary election because they are RINO's?
I'd imagine that quite a few of them. In Central CA, there's a big shake-up with an interesting campaign technique: candidates are campaigning as "Conservative for [insert_position_here]" rather than claiming any particular party. It will be interesting to see how well it works for them.
I would very much like to see more true conservatives in government. Liberal Republicans are just as bad as liberal Democrats.