On paper, the plate is not needed for deep snow. It gives you leverage (and hence more torque per effort) at the expense of added risk of injury in order to more effortlessly tip skis onto their edge. On a hard surface, like ice, you are torquing about the inside edge and the wider the ski the more torque you have to work against. On a soft surface that inside edge goes down into the snow and your pivot point is more underfoot.
I wouldn't bother with a lifter on a deep snow ski.