Cars are not a good analogy in my opinion. Classics aside the technology in cars has moved on considerably between that 25 year old Merc and a new car. The new car is probably much faster, much more efficient, has loads of modern tech and infotainment stuff. There is therefore many, many reasons to buy a new Merc over a 25 year old one (where that old car is just a regular model, not a classic).
iPhones aren't strictly a good example either.. the newer ones get faster, are capable of storing more, have funky features that no one actually needs, etc. That doesn't mean to say that I think they should cost £999+, but that's the price of entry at that end of the market and it seems people are willing to spend it.
What is the practical difference between most NIB pins and a B/W besides the LCD? A fully restored mint B/W pin may as well be new if practically everything has been replaced. Granted an actual 25 year old pin with 25 year old mechs, coils and wiring should be priced appropriately, but a fully restored one is essentially new to my mind.
My wider point, I think, is that in the grand scheme of things a pinball machine is a pinball machine. There has been very little innovation in them over the years ("if it ain't broke" ?), even the cabinets have stayed to all intents and purposes the same (bar widebody). Some pins have some extra toys, but older ones do too. The only standout improvement has been in big LCDs, and better sound. So in that respect, if a NIB Stern is selling for £7k, why should a B/W that offers the same intrinsic experience of pinball be worth just £hundreds? Or any pin for that matter.