I play a lot of GW2 so the first thing that comes to mind is having map specific events that come up based on Fates done on the map. Have a big cool event, maybe even just a more difficult Fate with good rewards, spawn if other Fates are done in the area. Chains of Fates that have a series of events that lead up to the big one. Something that people would want to do that isn't like hunts where it just randomly spawns every X number of hours. Might be too hard to implement but that's what would get me to bother doing Fates at level 70 when I'm bored and looking for something to do.