I think it can help you better brace yourself for impact. True punching power though comes from proper technique. Technique being range, using your entire body, proper rotation, and all the other little things that matter to generate force. The problem with gaining too much muscle is becoming musclebound, however some extremely strong individuals don't look like beefcakes anyways.
I agree with you in the sense that strength training can help, but without trained and practiced technique, it won't do much on it's own.