Like I said before, the current NIB market is primarily attributed to the Baby Boomer generation going into retirement.  People born between 1946 and 1964 are the most cashed-up and carefree generation at the moment. They played and subsidised arcades during the pinball 1970s golden era and are now reliving their childhood by creating home arcades of their own. They have other toys such as cars, bikes, boats and fancy homes. The NIB trend may continue for a few more years and probably a  HUO market glut in 15-30 years when deceased estates of Baby Boomers hit the markets.
How do I know this? I was born in 1959 and I can see what my friends and I are doing. Stern probably saw this when they hit the lows in early 2000s but hung on for the Baby Boom wave to hit the shores which they are now happily riding.