Well, I'm not going to speculate on the prowess of Stern's marketing dept. re: email lists of 30K competitive pinball players here, but it still feels like this is being grossly undervalued to me (I guess you mentioned that the email list is substantially smaller though as well).
My thinking is that the recent pinball resurgence is substantially due to the rapid rise of local competitive pinball tournaments, leagues, and most importantly, locations to play. I'm sure you understand all this, but bear with me while I illustrate my thinking and experiences.
Bad Old Days
Prior to this rise in competitive pinball the reason to put a game on location was to make $. But it became very difficult to make a profit putting new games on location due ot the high cost of the games, the costly and time-consuming ongoing maintance to keep the games playing well, and the lack of suitable locations willing to take a game. So gradually operators lost interest in further investing in either new games or maintance on older games, resulting in most games that could be found on location (fewer and farther between) being broken, dirty, and unpleasant to play. So it was a circle of doom resulting in the near extinction of pinball on location as people largely forgot that pinball was even still a thing (certainly no longer a mainstream thing).
Modern Pinball Resurgence
So then you have a small but growing group of pinball collector enthusists that maybe picked up a few broken older games as operatiors took them off location, who loved to play, but didn't have a way to do so in a public. Gradually the notion that you could organize a local tournament, or even a league with fellow enthusiasts starts to spread (thanks IFPA!), and lo-and-behold fairly quickly you've given pinball a new reason to exist on location and for people to play them regularily, outside of purely for fun.
Now, you have locations with 5-10 well maintained games springing up, a mix of older and modern games in excellent condition, ready to play, and groups of players willing to play them regularily for tournaments, league play, selfie-leagues, and of course practice/fun. As word spreads (thank you social media) more and more people discover they can play pinball in their town, join a league, etc. Thus, a virtuous circle is created where more competitive pinball = more nice games on location = more players = more new games purchased...
I have experienced this first-hand with my own early collecting days, struggling to find location pinball, meeting a group of like-minded enthusiasts in my town via one-off tournaments, forming a league with said individuals and working to spread the word, and eventually forming a collective and putting games on location ourselves to support our league and tournaments to ensure top quality games are available. Along the way, many old and new players have joined us, and many of these have purchased games of their own, and many of those games have been NiB games. NiB games that never would have been sold if they hadn't found our league along the way.
My long-winded point being that what the IFPA does/has done, in my opinion, is largely responsible for the recent resurgence in pinball popularity, and that the pinball vendors should be doing everything that they can to promote the growth of competitive pinball. Imagine if every state had as many games on location as Oregon and Washinton? What kind of value would that increase in market size have to the vendors? A lot more than $500/year. They should probably be sponsoring the state and national tournament prize pools with tens of thousands of dollars in prize money if that is what it takes to continue growing awareness of competitive pinball.