Still perhaps some towns/regular players could host events once in a while. Like the other day I noticed there was a spontaneous player hosted monopoly event which seemed to be pretty successful. Some other events might require mod or admin assistance of course, but others can be hosted by players themselves. Also if it would be possible for players to submit their events to admins, then they could possibly be posted in the announcements section on the forums. In that way more people may attend them. I'm personally willing to host a few events in my town if there's enough interest.
Event ideas that can be done without any assistance:
-Find the sign
-pvp (depending on the setup)
-spleef (would require tremendous amount of manual labour)
-monopoly?
-boat racing
-horse racing
-parties!
Event ideas that can be done with mod assistance:
-Fishing (inventory checking required)
-advanced pvp (inventory checking required)
Event ideas that can be done with admin assistance:
-Parkour (would require one time disabling of teleport related commands in a region)
-All the other stuff like cube, sand pit, etc.