Determining intentions by touch alone is crazy broken. Hidden intentions and secret plans are the meat and potatoes of good stories; the ability to see them with something as simple and easy as a touch thoroughly declaws them. I don't recommend giving him that kind of power.

Besides, Vali is only an antagonist, not a villain. Becoming her "minion" is not the worst thing that could happen. In fact, it opens up several interesting story possibilities on its own. Don't be so scared of losing to the antagonist that you lock yourself out of fun story material. :)