My BMW K1200LT has heated grips and a heated seat. The grips I use very frequently and probably won't have another bike without them. The seat on the other hand, sees very little use or do I see the benefit of it.
My butt never gets cold while riding, my chest, arms, legs, feet get cold but never my butt. Invest in a heated vest and pants before going to a heated seat.
My new RT has both as well. 39F in fog for a couple hours and was using the seat heater. Gerbings jacket as well. I'm convinced that it helps with maintaining core temperature. I wasn't wet but, if one is, the seat would help further.