I think that we are close to agreeing. This is a unique situation with important ramifications. The key is Kyl. If he wasn't next in line, I'd vote 3rd party as a protest. But protest votes still leave him in office. I've looked at this closely and everything about "R"len tells me that he has to go.
He has no respect for Republican values, let alone conservative ones. His votes 'with' us are most likely to fall into place during the final year of his term. If Clarence Thomas had been nominated a year AFTER the election, we'd all be saying Clarence WHO? Specter knew that he was under the microscope and needed conservative votes to win. He's spent a lot of time apologizing for it since.
The better strategy is to vote for Hoeffel. A vote for Hoeffel takes a vote away from Specter and gives one to Hoeffel which makes a difference of two votes and that' s like two votes less for Specter. A vote for a third party candidate takes a vote away from Specter, leaving a difference of one vote between Hoeffel and Specter.