Highly limited offerings are essential. At some of the best places you can only get one thing (usually tacos), but limited menus in general tend to promise imminent delight. Hot Doug's is an obvious example as is Kuma's Corner (you could get something besides a burger, but you'd be stupid) and Johnny's Tavern has a full bar, but you'll never see anyone with anything besides whatever Czech beer Johnny is handing out that night. Other important factors are difficulty of access and odd hours. We love to be abused!
The rules function in a few different ways. Most important of these may be the way in which they immediately highlight regulars: anyone who already knows all the rules belongs there, and tourists or first-timers stick out strongly. I also just like the ceremony of it all. Surmounting the hassle makes it all just taste a little sweeter. Importantly though, and I hope this isn't too much of a stretch, the place has to deliver on its own terms. Like "Hamlet on Mars," if the only thing you can say about a place is all the hoops you have to jump through once you get there, no one is going to go. The food has to be worth it. The adventure of a place like Johnny's might be enough to get a few new people in the door every weekend but if that Czech beer weren't great, or Johnny so charming no one would go back a second time.
The narrative of attendance, then, that is so important to marketing-- "what is going there?," "why should I go there?," "who else goes there?" -- fails if the art fails. We are just so desperate for that product that we are willing to submit to the precedence of these minutia in our search.
I guess I'd be stupid if I didn't link to some Soup Nazi, enjoy.