Being new to the Model X community (coming from a 3), I’m a little intrigued by your post. Consider that the OP probably paid $50k vs. $90k. How will he be paying more, overall, to drive an older car? I guess if you’re talking “lease”, then maybe I get it. Otherwise, I’m confused and curious to know.
DISCLAIMER - Below I am going to make a several assumptions that seem reasonable to me, but I am sure that not everyone will agree with them. If you think that my assumptions are off, feel free to insert your own numbers. I am not advocating that my assumptions are 100% accurate. My advise is just pick some numbers and think about the value before you dive in. Just because a car is less expensive than others on the market doesn't necessarily mean that it is a great value.
How long do you think these cars will last? For a number of reasons, I don't think these cars are going to last much longer than 8-12 years. If you buy a used car from Tesla and get an additional 4-year warranty, you are pretty much guaranteed that the car will make it to 8. So I will go with 10 years. You might get lucky and it could last a few more years, but I don't want to plan on getting lucky.
So with a 10 year lifespan.
A new 2020 Long Range Plus costs: 85K / 10 = 8,500 per year, and a 4 year old car at 50K costs 50K / 6 = 8,333 per year.
So that used car is not more expensive than the new one, but it is essentially the same price as a new car. Already a pretty bad deal in my book - I want a substantial discount if I am going to miss out on the new car smell.
BUT - that is comparing a 2016 75D to a 2020 Long Range Plus. Those are not equivalent cars! Many things that were optional in 2016 (and not included in the lower priced used cars) are now included standard in 2020. Things like leather seats, heated (rear) seats, heated steering wheel, automatic doors, bioweapon mode, etc are frequently missing from the lower priced used cars. Additionally, Tesla has discontinued the smaller battery model X's. A 2016 75D only had a 238 mile range. A 2020 X has a 350 mile range. That is a HUGE difference. Using the price of a 2020 Long Range Plus to calculate the value of a used 75D makes about as much sense as using the price of a new Model S to calculate the value of a used Model 3.
If Tesla still sold a car today with the options and range of a 2016 75D, it would probably be priced under $70K. So even though you can't buy it, the more fair comparison is a a new car at 70, vs a 4-year old car for 50K. If you do the math that way: you are looking at 7K / year for new vs 8.3K / year for a used car. Thats crazy. Personally, the price would have to drop below 6K/year = 36K before I would consider a 2016 75D a great deal.
Again, you could very reasonably pick different numbers and with different assumptions you might come to a very different conclusion. Given the current market value of used X's clearly most people value these cars way more than I do. I don't think that anyone needs to agree with my numbers, but I do think that every used car buyer should think about the annual cost instead of just looking at the total vehicle price.