I agree with @ohaq. They are starting to get pricey. Some of the people who have posted use them a lot more than I have. We've used our rear-facing seats an average of once/3-4 months for a short trip in town. I will admit that sometimes with a car full of our kids' amazed friends, it does seem worth it, but not for $3000 at that frequency of use. I've thought that maybe as my kids get older and I'm shuttling them around more often to sports/activities with their friends we might use them more, but at that point they might be too tall or would prefer the ease of using the 2nd row (assuming 5 or less people in the car). Also, at least for me, I feel a need to lift them into the rear-facing seats to avoid scratching the paint near the bumper (even with PPF), so that's a bit inconvenient.
Although, I know they are supposed to be the "safest seats in the car", I've always had quiet concern for the proximity of the occupant's head to the rear hatch glass eg if a taller truck runs into the back or if a car "ramps" up the rear hatch in a collision. Not trying to spread fear, just expressing what I've thought to be common sense. Finally, between that rear row and the double-reinforced bumper, I'd be surprised if the two don't add 150-200 lbs to the weight of the car.
Having said all that, I do think the rear-facing seats are a novelty or collector's item for the Model S, in addition to practical benefits. And that, for this car, is good enough reason to make it worth it.
