Depends on the time of year. When it's summer and I'm driving someplace, I think whoever invented air-conditioning for cars deserves a Nobel Prize, or sainthood (depends on how hot out it actually is; and no, I do not want a fried egg sandwich). During the winter months, I champion the cause of whomever invented seat warmers.
If I had to pick something, the one thing that demarcates (is that even a word?) the difference between 'why, yes I am an American--did you want to see my Gold Card?' and basically all the luckless, lunchless, little ones (I always forget how much I love TK and I'm not all that sure exactly where the cat is) across the globe---and I'm NOT allowed to use Paris Hilton as my example--I'd be tempted to use car seat warmers (or vehicle seat warmers, I guess, if you drive something other than a car. I'm automatically assuming motorcycles have such a thing; as a matter of fact, it follows as day the night, they'd have had them years before the rest of us).
I admit having the little washers and wipers for the headlights is pretty spiffy, as is having the side mirrors that automatically redirect when you put the vehicle in reverse, but there's a level of usefulness that dulls the edginess of those nifty options. I want something closer to a disco ball hanging from the rear-view mirror; something that says 'HA!' in the face of the question 'what do you need that for? ' and I'm thinking seat warmers are a good fit.
Let's be blunt and candid. Of course, they work when no one is seated on them, but they're not really seat warmers, they're backside (or other words beginning with B) warmers. Some cars, though not mine, have a type that warms you in the winter and cools you in the summer. Talk about 'let them eat cake'! Now, we have a drive-thru for that, and pie as well.
My seat warmers have two temperatures (I almost typed 'speeds'), toasty and well-done (I think) and as I've aged, I've concluded 'toasty' is like using 'regular strength Tylenol' as opposed to Extra-Strength ('Nope,' I say, 'I don't want that headache to go completely away, really fast. I'd like the pain to linger a little bit so 'regular strength' is just fine, thanks!'). Now I go directly to the 'yipes! That does get hot, doesn't it?' setting since the winter cold isn't exactly letting up anytime soon.
And, because what were once vices are now habits, I already know, should I ever seek out another car, I'm planning on seat warmers with heated backs AND headrests. After all, if it's NOT conspicuous consumption, is it still consumption?