I don't care what Republicans do, but I feel it's unacceptable to send Republicans to the senate over Democrats in a competitive senate election if you consider yourself a Democrat.
I dunno; take Rhode Island, for example. I like Sheldon Whitehouse and think he'd be a fine senator, but I really don't have the heart to kick Lincoln Chaffee out. After all, he was smarter than most Democrats (and myself, unfortunately) when it came to the Iraq War.
However, I definitely support Menendez over Kean. If this race didn't matter, I'd probably consider Kean (although he really does seem quite dumb).
The individual candidates don't matter. Voting for Chafee allows the GOP to maintain committee chairmanships and so on. Too much is at stake for you to back Chafee because you like him. Chafee's alright, but a vote for him is a vote for Coburn and Bush and Cheney and the entire Republican party.