Agreed 100%. I do the exact same thing - never buy a car brand new - the depreciation hit is just insane. I got my 2016 Model S75D 4 months ago with every option (other than the upgraded sound system) and FUSC, 4 year/50K miles new warranty from Tesla with only 16K miles and it cost half of what the first owner paid for it. The car is in amazing condition - it still has the new car leather smell.
I deliberately "gave up" on a newer MCU/AP as those cars were easily $15K more and were not worth it in my opinion for the incremental improvement.
You paid $63K USD for a used 2016 S75D. Sorry that isn't that great a deal. What someone originally paid means absolutely nothing.
You could get a brand new S for $78K USD ($2K USA Tax Break), with everything, including FUSC and Premium Audio.
It's also a much better car. New Suspension, Raven, Bigger Battery than yours, 373 miles range, New MCU, New HW3.
So, my mind you didn't save anything, you just got
way less car, for arguably to much money.
Here is another way to look at it.
For simplicity sake lets say you keep your 2016 for 3 years. You'd be driving a 6 year old car by the end.
That comes to $21K / year to own.
Buy a new Model S at let's even say $90k with some extra goodies. And you keep it for the same 6 years (the same oldest you'd want to drive in).
That comes to $15K / year to own. And you had a newer/better car for the first 3 years.
How are you saving buying used again?