Kubel isn't close to being ready to put up all star numbers. He's basically a rookie and blew his entire knee out about a year ago. I'd be surprised if he puts up any sort of decent #'s this year, and I do believe he'll be an all-star someday or at least a solid starter.
This is a solid move, he's 5-6 years younger then Piazza/Thomas and in a full time DH role (maybe some switches with Stew to save his hammy's) can put up 450-500 AB's I think, which should be good for 280/20, which my friends are pretty sweet numbers on the Twins. It will provide a nice alternative to Hunter for filler between the M&M boys too.
Also, if he can stay healthy, can help replace Jones' power and unlike Jones won't be an easy out if a lefty comes in as White is effective from both sides.
It's a decent move that's VERY low risk and it's a move that "poor" good teams make. We can't trade for the Delgado's and don't overpay for the Giles. It's not ideal, but probably is the best they can do with what they have available.