Being able to access good content freely leads to over playing Over playing leads to boredom. Boredom leads to me trolling this boards because I'm fed up with all the other MMOs I've played LOL.
1. Rare dynamic events. I don't mean this spawns ever hour. I mean this spawns every month. Players would hunt these events like Ahab hunted the White Whale. Players would research how to make this event spawn on the wiki's and watch videos on it. You want an example? How about cultists have kidnapped a girl, and are planning on sacrificing her to The Spinner in Darkness. If you save the girl, The Spinner (no not that kind of spinner :P) comes through the portal and attacks everything. The Spinner is a massive spider, that acts like a spider. She is large enough to straddle the road, and can walk up the walls of buildings. If she isn't immediately killed she starts weaving a web between two skyscrapers and laying eggs. The eggs hatch and more spiders come out. If she isn't stopped she can over run the neighborhood.
2. Unlock-able dungeons. Some dungeons may need keys to open them. These keys could be fairly rare drops, or they could be a difficult puzzle that only spawns once an hour. Ideally, these dungeons would be open to the public so if a player does a zone wide call for call for help everyone could come and help. An example could be first players need to get a gem of seeing. The gem could be a very rare drop from this one kind of enemy. Players would then equip the gem and use it. Most everything looks normal while looking through the gem, except for some areas have doors that are lined in golden fire when seen through the gem. Keys are found be defeating raid bosses. The key and gem are consumed by opening the door. No one knows what's behind the doors.
3. Rare super events. Rare super events are differentiated from rare dynamic events because they completely take over a district of Titan City, and they aren't player activated. An example is an alien invasion. The invasion would displace all the content in a certain area until the heroes won the battle. The invasion would fire back up in six months in a different district. This could be a lure to get inactive players back in the game by broadcasting the reactivation of the event on twitter and facebook