No regrets here. I bought a used 2013 M85 from Tesla Used division. It was in pristine condition, 30K miles, and was the flagship of its day. MS has come a long way since my MS was made, but I love my car, and have no regrets. I have learned a lot about Tesla, about EV's, and am formulating my next move, which will probably be a M3P, or maybe an MYP, but I am happy with my MS85 right now. Tesla has been very good to me as far as service. I've only taken it in for a few things, but they covered it all under warranty except for an alignment, which it didn't really need but I felt like it did... Sure, I kinda wish now I'd bought a newer model, maybe a post-facelift 90D at least, with AP and air suspension, but I am fine without those for now.
On the subject of the "next vehicle" - why the M3 or MY instead of an new MS?? I spend about 95% of the miles I drive alone in the car, and for the other 5% there's usually only 2 of us, RARELY a 3rd or 4th person. Seriously, I can count how many times someone has been in the back seat. So, it makes no sense to have a car that big and heave for one person to mostly go back and forth to work. A smaller, lighter, more efficient car makes good sense. I think Tesla has moved on from the MS and the MX... the M3 and MY are the vehicles of their immediate future. The battery technology of the MS/MX is old and inferior, the AP/FSD hardware is behind the curve compared with the M3/MY. Those are my main reasons, Size/effeiciency, Batter tech, AP/FSD tech.... oh, and cost.
I will be forever in love with my MS, and I would love a new MS Performance, but I think that unless they change to a new battery technology, the MS/MX will become an obsolete niche model.