The report that I saw was odd. In a very Ivan Drago, Rocky IV sort of comment, Helton said, "I am strong like a bull." But he qualified the statement by adding something like, "at least I hope so." Supposedly, he added muscle rather than lard.
Since he's not a speedster, you've got to figure that the weight doesn't rob him of SBs. He'll probably hit a few more HRs but have a slightly lower AVG from being (even) less able to beat out ground balls. On balance, a slight plus, but not a meaningful factor for me. Also, I'm hesitant to ascribe much credibility to the report without knowing more details about how he gained the weight, where he worked out, etc.; you don't hear many athletes saying, "I bulked up on Doritos and Mountain Dew over the offseason," so until we see whether he's blasting 500 foot homers in spring training every day, he's not moving up or down much for me.