How about this type of mechanic for spreading out new content so it lasts a while longer. Tie a series of quests loosely together, with the following caveat. The mystic/runic/whatever entrance to quest 2 will only unlock after someone on the server has completed quest 1 and started the unlock timer.
Right now they have a quest timer mechanic in place to repeat various raids and a global broadcast of raid success method as well. So what this would do, is whenever anyone on the server completes quest 1, it triggers a server wide unlocking of the timer for quest 2 and receives a server wide broadcast reflecting that success. Some period of time later, it could be a few days, or even a week later, the portal to Quest 2 is now accessible to everyone on the server. Rinse and repeat with quests 3 and 4, etc. You now have some weeks of quest anticipation and planning, based on the first parts and can make the new content be new for more than 24 hours.
Make completing the quests in sequence open of a nice end reward (kind of like finishing VONs), or the Litany series, but give each quest a decent reason for being run on its own as well (reasonable chests or some token of some nature that can be turned in ala BAM or Invaders). (Lots of people would run VON3 repeatedly if they could I suspect.) Perhaps to open quest 2, someone in the party needs to have the end token from Quest 1 to activate the portal (or at least the proper quest completion setting in their favor log.)