Though I hold substantially less esteem for Senator Spector since he left the GOP, it must be said that being a moderate ain't much fun these days.
As difficult as it is to be a moderate Republican, the gods of politics do not look favorably upon party-switchers. He would have been better off fighting to the bitter end in the GOP primary and at least being a standard-bearer for the dwindling numbers of voters who long for statesmenship and virtue instead of ideological madness and vitriol.
I think his chances would have been better if he'd just gone indy and then caucused with the Democrats instead of a full blown party switch. Switching parties opens you up to more accusations of hypocrisy than going indy does. Granted, Pennsylvania is probably a hard state to run in without a party but I think Specter could have pulled it off.
Actually, come to think of it, this is what the moderates should have done from the beginning. Specter, Collins, and Snowe should have all left the GOP simultaneously and created their own party. I'm sure they could have gotten some house members to join them as well.