I think you've got a lot of different factors at work here. Do you have new pins coming to the market? Yes. But most of these pins aren't being purchased by operators, they are being purchased by collectors. The existing pins that are out there from B/W for the most part were routed. Those pins were already paid off on route and made money for the purchaser. When the operators sold them off they had made their money off of them and whatever they got from them when sold was an extra. If they bought them at $3500, they weren't going to sell them for $2000. Who would buy them? Plus, the market to own a pinball machine wasn't there like it is now. You could go out on location and play the latest and greatest table for $.50, $.75, whatever, and you didn't have to haul it to your house, pay for the upkeep, learn to work on it, etc.
Fast forward to today. Pins for the most part aren't being purchased to be routed. Collectors are buying them for multiple reasons; you can't hardly find pinball in the wild anymore, kids from the 70's, 80's, and 90's are older and have the disposable income to afford to own pinball machines, plus they want to recapture a little of their youth, etc. For the most part, if you want to play pinball, true pinball, you need to buy a machine, or know someone who owns machines. Stern knows the collector market is where the money is to be made now, and are catering to that crowd. Gone are the days when they could sell a run of 10K machines to operators, they aren't out there anymore. So instead of selling 10K widgets for $50 for example, they are trying to sell 2000 widgets for $200. They've had to raise prices to make money, plus to satisfy the pinball collector rather than the operator, the LE's are sporting more toys, etc. Used NIB pins are not going to be sold like routed pins were, as they haven't made the purchaser any money. Sure, some have depreciated, but some are appreciating in value. If I spend $6K on a NIB pin, as a collector I'm not going to sell it for $1500, it hasn't earned me a dime, and it should be in damn good shape.
As pinball collecting becomes more popular, the demand for the older pins has gone up, and so have the prices. The alternate is a NIB pin. As people above have said, many new hobbyist aren't willing to spend $5K and up for a pin, so they look for the older machines, driving the price higher. The last of the operators for the most part know what the market is for routed games and as they get out of the business or turn over their "fleet", they can get more for their pins selling to hobbyist. It's a catch 22 for them, as it's harder and harder for them to make money on location with new pins due to the costs.
JJP and JPOP/Ben Heck have seen what collectors are willing to shell out and they are getting a piece of the market. JJP has said that they have a plan for their pins to be operated profitably, we'll see. I personally think that pinball in the "wild" is dead, and isn't coming back, but we'll see.
Bottom line is, since the supply of routed "cheap" pins is all but gone, I can't see how pin prices will go down. Pinball is now a boutique hobby market and will be priced accordingly.
Edit: I see as I wrote my book this thread has grown.