This is interesting to me, because I'm generally in the "buy new" category for most things. I generally like to buy new cars (even though I _know_ it's wasteful), and I'd rather have a new BMW than a used Ferrari, and I'll make myself feel better by holding onto it for 15 years. It's nice to option out things exactly the way you want, and it's fun to be the first owner and to treat it "your way." There's also the big bonus of a warranty. I was very surprised to find myself in a 30 year old airplane given that I had a roughly million-dollar budget. There's no ardor like that of the newly-converted, so here's my thinking:
Airplanes are a somewhat unusual case because the more expensive stuff is so often objectively more capable. A Maserati, a Lexus, and a Ford are all going to get me to work reliably, safely, and at about the same time. The only reason to buy the higher end stuff is because you just want something nicer and fancier, and "new" is nicer and fancier. A used TBM, on the other hand, is massively more capable than a new DA62, and they're the same price. The TBM _will_ get you there way more quickly and in more situations than the 62. My (admittedly ancient) Aerostar is just in a different league than a new Mooney or Cirrus. They're not even close in terms of capability and mission flexibility, and the extra $400,000 that I didn't spend pays for a lot of maintenance and fuel. Everyone throws out "tax," which is true to an extent, but you can still depreciate used aircraft if you structure it properly, and if it's business use, you can deduct maintenance, too. At the end, you still have less money than the guy who purchased the cheaper aircraft to begin with.
There's also a _really high_ market ceiling with airplanes. Even if you have $5mm to spend, wouldn't you rather have a used jet instead of a new King Air in most cases? Even the ultra-wealthy (Google founders, celebrities, etc.) tend to buy used airplanes, because the performance increases tend to be overwhelmingly desirable. Rich enough to buy a new King Air? Buy a used Citation. Rich enough to buy a new Citation? Buy a used Gulfstream. Rich enough to buy a new Gulfstream? Buy a used airliner and put a swimming pool in it.