Since Joe Sestak is not going to run for reelection to his house seat and instead focus on running for the Democratic nomination to the U.S. Senate, shouldn't he just resign?

Doing so would allow Ed Rendell to appoint a Democratic successor to hold the seat and run as a semi-incumbent next year. And it would give the 7th District a representative focused more on doing his job than running for higher office.

Or is it more important to Joe to collect his congressional salary and benefits (plus his Navy pension) while campaigning for Arlen Specter's job?

Just askin'

UPDATE/Correction: Oops. The governor only appoints senators. If a congressman steps down there has to be a special election. I'm OK with that.