You are exactly wrong. Not only do I doubt this is Specter's last term (provided his health holds up), but if it is he's going to be even farther left, even meaner, and even more aggressive about his personal agenda with no Republican primary to look forward to in 2011.
Since 2000, Specter has been voting more to the right than his previous incarnations.
See his ACU record.
I still don't like him, but lets see where things go.