I hope Minnesota does get a new ballpark. I've been to the dome and it certainly doesn't feel like you're watching a baseball game there. Anything that is good for baseball anywhere I'm all for.
As for the affect on the Sox, it shouldn't matter. The Sox have to worry about getting their fans to come to the Cell. Chicago is a larger market than Minnesota and if the Sox management does their job well, they won't have to worry about Minnesota's new stadium causing problems for the Sox.