[plamzi]

There is really no way to take on the "been there, done that" syndrome by simply adding more stuff. Most players develop it long before they actually burn through the content (the more they grind...) so adding new content is not going to change their subjective impression that they've seen it all before.

One thing I've found is certain top-level mortals naturally mature into mentors of newer players and enjoy that role. Any tools or in-game incentives you can offer to help them mentor more effectively will not only extend their end game, but have the potential to build your community (since knowledge transfer is essential).

When I was designing our custom quest system, the main goal was to enable mortals who have grown extremely familiar with the world to easily create quests for the enjoyment of others without having to take up formal staff positions. This falls into the user content category KaVir mentioned earlier. Every published user-contributed quest is signed with its author's name, which makes it part of this player's legacy.