I've found one of the more annoying parts of building rockets is making sure that the rcs has been perfectly about the center of mass so that there is no rotation when I translate from side to side. This is a very minute issue, but one that could be remedied by adding a feature for mirroring objects about the center of mass. just a thought.
I think that a tool that shows the torque induced by the RCS will be more useful. This way it will allow you to be more creative and also allow you to eliminate any RCS (or main engine) induced torque.