Heated handgrips is a bit overrated IMO. I have them and yah they feel nice on the BOTTOM of your hands, but the wind blows over the top so only half your hand is comfy. What I do is turn em all the way up to hot hot HOT and let the heat hopefully heat up the entire glove and hopefully radiate thru a bit but if you got ANY moisture in your glove, sweat... it's misery when it gets below freezing.
heated seats now, I do NOT have but sounds like they would be very nice, all that heat goes straight up into your chilly ass. But again, can it really make it thru a good set of leathers if you got them on? If you are wearing regular pants, the rest of you is freezing anyways so the hot a hole might be pretty much .. negligible.
Aaron