I hosted an event for coworkers the other day at a well known D.C. Pinball friendly place. All of them had fun, but all of them explained they thought you were Just supposed to bash the ball around and not drain, but didn't understand strategy or how to use the flippers for catches and such.
I played a game projected on the tv screen in front of everybody (the place has a camera on .. Avatar, I think) and suddenly the light bulb went off. IMO quarters were a huge detriment to the "next game" - every time they had to stop and grab quarters, make change, event just put them in the game, they were this close to stopping. Those cards they use at Dave And Busters are genius because you don't really know how much you have on there. Somehow we gotta get credit cards in the mix.
Alternately, free play for an hour works REALLY well. There's a place near Tampa we go to that's $10 for all you can play. Kids become pinball fans there because they have time to learn. I've seen it happen with our friends' kids (my son doesn't count since we have 4 games at home)
Last thing - somebody mentioned comic con. I played Ghostbusters at a comic con a couple years ago, which started this whole mess. Put a themed game somewhere unexpected, like a comic book shop or record store. It will be a hassle but you will catch your most likely audience there, and they may come check out your other locations.