I don't see the numbers of Sterns for sale being anywhere near the 1990s pins u see up for sale. I would have said not even close. I think times are tough for some people and they spend 6 or 7 grand then either need money in a hurry or decide to sell one pin to buy 3 cheaper titles. Also, operators always try to pass sited machines off as home machines only.
Some people don't seem to mind buying a new in box pinball, they play it for 12 or 18 months, get bored and move it on and lose $1500 or $2000. But at the same time, they sell a ACDC and then buy a Star Trek Pro for the same money, so they move sideways so to speak and get something new to play.
Pro rata, I reckon 80 percent of BNIB pins stay in collections for decent periods of time being 3 to 5 yrs plus. All the guys I know who regularly buy new Sterns keep them. Of say about 6 or 8 people, only 1 mate moves sideways every 18 months.
Either way, most Sterns usually don't have a problem getting $4500 to $5000 plus for good examples. There's probably only a few hundred of each model brought in each year, being the Pro models, and a half to third of that being the LE or Premium model. You only see apx half a dozen per annum being sold if they are home use only. Perhaps some get sold privately between collections without an advert ever being seen by the public. I am sure some collectors probably swap sterns for sterns as well. Either way, they all seem to be holding their value quite well and usually sell quite quickly. So the Stern resale values are still excellent IMHO. Food for thought....