Is mileage a big factor in my searching? I know battery is but how would know if they were abused or good for 500k+ miles?
I think mileage is a main factor affecting the price and is a good estimate of age of the moving components. But there are exceptions, I think, such as if major components had been replaced. Most of the older performance motor have had their motor replaced, I believe, due to design flaws that caused the early bearing failure and coolant infiltration. In those cases, their longevity reset a bit, I would guess. My 2014 P85+ is ancient, relatively, but it drives and feels like a new car. On abuse, one would never know for sure, I think. Two things that I do when buying a used car to minimize the chance of getting an abused one are only buy the ones that has one previous owner and test drive before buying. My guess is that the 60s are increasingly less desirable due to the low range. On AP stuff, I enjoy driving so a performance non-AP rear-wheel drive with ‘plus’ suspension and staggered wheels has been the best Tesla I have driven (although I haven't driven all variations). On seats, yeah, the newer seats are better. It was the only thing I didn't like in my MS’s, but I have gotten used to them and now don't mind it. On roofs, I have the pano roof (glass with sunroof) but it hasn’t had any problems yet. On MCUs, I upgraded one to MCU2 (I paid $2500, but they are now $1500), and on the other one, I had the daughterboard upgrade (I paid $350, but they should be free now). I have been happy with both.