I recommend you check out the Strengthening discussion. Generally, Strength Training is very advantageous, if done properly, but it does not necessarily mean you have to use weights (e.g. proper bag work, calisthetics, etc). You can use weights as well, but strenghen your muscles, don't "bulk" them up - keep your muscles long and don't lose flexibility (which you need so much of in Wing Chun). You can do this by using low weights and high repetition - this will develop their flexibility (with strecthing, of course), and keep your muscles elongated rather than bulk and shrink them. You will keep the maneuverability which your style (like any other, for that matter) requires. Anyways - read more in the Strenghening discussion.
Keep your guard up!