Have some daily challenges, maybe weekly also, that are random and individual.
1) gives you a reason to log on every day (not just scan the webpage to see if an event has appeared without warning)
2) means the players aren't all doing the same thing at the same time
Just make them like event type goals with scaled rewards based on how of a much challenge it is.
Still have events, but they can be more themed/specific (or meaningful in some other way) than just "1000 damage with missiles" and the ilk.
I know it's wishful to hope for, but if it's easy enough, PGI, do it.
