The only pins I see increasing in price, are new Sterns, and this is do to the drop in production.  If Stern could sell 5000 of one title the price would go way down, but the vendor is not buying pins for there route anymore, so the homeowner is there main customer.  I have sold a few pins to Australian customers, and with shipping it was still less expensive then buying in Australia. 

Curly

Little Shop Of Games
Pinball Sales,
Parts, and Service
3635 Eagles Nest Rd
Fruitland Park FL 34731
561-248-9628
www.littleshopofgames.com

The only sterns I can see increasing in price are possibly elvis and playboy. This will be when stern go out of production and will be 10 years after that. I have seen several titles sell under 4k, (these are still late model pins). Cannot see many topping the average $7000 purchase price, thats just my opinion.