Sounds like you answered your own question.
Kean's only value, if elected, will be as a placeholder, much as Lincoln Chafee is now. I.e. Kean will be simply one more warm body to add toward a total of 51 Republican senators, to hold the majority.
Kean if elected will be a royal pain in the arse. He likely will not vote for excellent SCOTUS nominees like Sam Alito (Chafee didn't).
He will be a thorn in the side of President Bush, just as Arlen Specter is now, only even more annoying because he's a cocky smartass kid.
That said, yes, I am going to vote for Kean.