I've never felt the need for heated seats on a bike or in a car. By the nature of the materials they are made of seats are quite insulating and in a fairly sheltered position, so don't drain the heat out of your nether regions, especially if you are dressed appropriately with two or three layers. If switched on well before you first sit on the bike, heated seats may provide the luxury of avoiding the initial shock of sitting on a cold seat, but I can't see that there is really any need for ongoing heating throughout a journey. In contrast your hands are on probably the most exposed part of the bike with no insulation from the heat draining metal bars other than a thin rubber grip, unless you have heated grips - so I regard them as essential.