To answer your questions @swervit
A: No. For 99% of us we are not stacked and stable on our skis ALL the time. Bringing your centre of mass over the ski, for the most part is a good thing and if HEEL lifts allow you to do that, go for it.
B: I dont personally see a need for it, ive got too much other stuff to worry about. If I was to do it, I would probably only do my rear foot.
C: Heel lifts generally allow for accommodation of reduced ranges of motion in joints of your feet. Greater freedom and range of movement in your joints, I think, can be had by pivoting both your front and rear boots.