Well, Gordon, looks like you triggered a discussion here...
I was going to post some thoughts about this unexpected attendance and the possible theories behind it, but didn't want pollute AP with such hyperbolic thoughts. But your post got me motivated.
First of all, this is a urban park, adjacent to a highly educated and somewhat affluent demographic. The park is somewhat large, considering the proximity to a high-density residential area, and has areas with a definite wilderness aspect, and terrain features that make it look wild, like steep slopes and cliffs.
On one side, the demographic are academics, doctors, lawyers, bankers, public figures, and on the other side the demographic is low income and chronic social issues.
The park is heavily cherished by its users: hikers, bird watchers, dog owners, families with children, mountain bikers, runners, nature lovers, city people that don't own cars.
Novelty factor: nobody heard of "orienteering" and hardly used "topographic map".
Presence of an alternative charter school called "Environmental Charter School", a place of schooling that has become "fashionable" among those that see the non-traditional teaching and learning opportunities that exploits the park in the school backyard as a teaching classroom.
A plug-in by an influential blog
and its 4 minute of airtime on a 6:45 AM Friday annoucement on a rock music radio station
Fliers on bulletin boards, libraries, utility poles, laundromats, business show windows, hand-out to folks standing on line at REI store garage sale events, monthly meetings of outdoor clubs such as the mushroom club, geocaching club, explorers, hashers, mtbikers.
... and then, the internet-based social media factor, like Meetup and Facebook and email-based groups.
And yes, only one O-suit. As a matter of fact, very few people of the "usual suspects" participated: the mountain bikers were on their own thing, for the hashers it was too early in the day and no beer, the adventure racers saw it as a gimmick being not a true wilderness endurance event.
The great majority of participants were families. Kids. Mothers. Fathers. Communities of friends. An excuse to do something pleasant outdoors. Do something with other friends. School friends.
The event did run out of maps. But because of a fortuitous request of a private printing of a set of 50 extra maps, it was possible to use that stash of non-planned maps to draw the White course on. One volunteer was suddenly deputized to do just that. No one got turned away.
The parking lot was full and additional vehicles were parked not-exactly-legal. Luckily nobody got ticketed. Others parked in the city streets and walked a longer distance to the registration.
And yes, fire hydrants are cool. Specially those vintage ones, in the middle of nowhere. Past vestige of past civilizations in the Planet of the Apes. The Fricks, Carnegies, and Mellons used this land as their playground and golf tournaments in the age of the Steel Industry.
We hope that a "buzz" gets created, and that these newbies and first-timers come to our regular meets, out in remote places like state parks, reachable only by car.
Incidentally, a few years ago a bunch of Carnegie Mellon students and others volunteered on an experimental scavenger hunt project in this very identical park. The idea was funded by Disney, researching new ways to entertain people. Don't know the results or outcomes.
In our event, we used old-fashioned paper and compass, technologies that the ancient Greeks and Phoenicians used two millennia ago, and looks like we succeeded in equally entertaining.