Meeh, well, a possibility that came to mind this instant might be that we have a more active and OOC-way of preparing quests.
I've tried it before on another server and it worked for some time, numbers and activity rose as a result.
idea:
Make a post where people give an open idea of a quest for discussion, or possibly a DM whom feels for it makes a list of possible events. People can then either add themselves or people who voice themselves on the forum can agree on a date and time for that event. People can then meet up at that time.
Now it isn't the most elegant or plausible solution, given that it involves a lot of OOC preparation, but it's a means to an end.
Bonus:
-Players & DMs alike may find inspiration in the ideas of others and thus come up with new events from that, spawning a huge number of quests that could be available.
-Players & DMs could center their online time to make sure that as few as possible stand around for hours waiting for others logging on.
-Possible increased activity as a bi-product.
-Regular quests makes new arrivals stick around.
Minus:
-DMs may suffer from more work.
-The idea fails and some may loose hope entirely.
-The idea is too OOC for a number of people and thus scare them away from the server.
-Players get too used to quests and thus demand more and more, thus once more increasing the amount of work for DMs.
-Time given to these quests may steal time from Main Plot lines.
-Players get their "needs" satisfied during the quest-time and thus refrain from logging onto the server unless there's a scheduled event. (The difference from the current situation is blurry though)
Now, none of these quests have to be big and world-altering, they could for a fact just be a small encounter, say help an old lady get her cat down from the tree (who wouldn't want to use Hellball in that situation?).
As a note, once the quests have been submitted on the forum they could be made more IC as a sort of "Quest-board", a slight modification would be in order at that point, as in having the DMs first sign in to whatever quest and then discuss with interested players a time and date.
Just a idea, take it or leave it