My 2 cents...
My son has always been a great contact hitter but was always fairly tall in his stance. This year, however, he started to squat just a bit in his stance. When he started doing this he widened his feet a bit, too. I'm not normally one for messing with a good thing - his old stance seemed to work just fine for him as he isn't real big and I didn't think of him as a power hitter. But, with his slightly squat, widened stance he is really exploding into the pitches. He has almost as many extra base hits as he does singles. And Elliott is right - it all comes from the hip rotation and the torque explosion as you attack the ball.
Sorry, this is getting a bit long, but I wish someone had me widen my stance when I was younger. I had a tall stance and took a big stride into the pitch. That really caused a drastic change in eye level as the ball approached. I really had to make a big adjustment during my swing. With the wider stance, I notice my son's head stays at about the same height all during his swing. He doesn't need to adjust his eye level to the pitch - it pretty much stays the same and seems to make it easier for him to track the ball all the way to the bat.
