EG,
The movement and location etc... are very important, however velocity is right up there with them. Once your arm is in good shape you should not be underthrowing just to try and save your arm. The best way to develop your arm strength is long toss number 1, but throwing fastballs number 2.
You also must teach your body to work at game speed. That's great that you can hit spots at 70 percent but when you crank it up during season, your body will be working at a much faster rate. From that perspective alone you should be teaching your body to work at "game speed."
Just remember to have your arm in good shape before you crank it up. No need to hurt yourself!
"Forget the curveball Ricky, give em the heater."