This could be fun but its kind of a bad idea for two reasons: 1 If you make it completely open you would end up with a very crowded park, and no one likes a crowded park. 2 Being invited to events like these is kind of an honor to some. If everyone is invited it leaves for no sense of pride or achievement.
open events are sick though. but even events like snowboarder super park arent completely open. it could be sick if it were done right and everyone in attendance was having a good time.