Really no conclusive outcome. I refuse to pay $100 each for the sensors. I have a second set of wheels with snow tires now on my 4R and no sensors and so far no light.
I have been told the only time the system will "see" the problem with no sensors is when I have been on the road for 45 minutes or more - then the light will come on. So far I haven't been anywhere but around town since I did the swap and so far no light. But I doubt I've been on the road for 45 minutes or longer continuously so perhaps the light will come on when I take my next long ride.
I was able to buy 2 sensors for $25 each on eBay but I haven't seen any more come up for sale since. Two isn't any better than none so right now they are just sitting in my desk drawer. If I can cop two more maybe I'll add them to my second set of wheels - or not!
So far the 4R hasn't blown up without them - the wheels all still turn, the motor runs, the heater heats, etc. So in conclusion, I'm not sweating it.