Pretty much major holidays will always see some kind of contest, egg hunt, pumpkin hunt, christmas tree decoration, lovey dovey valentine stuff, etc.

Also, if you're after a chance at bonus expee there is usually a note or two regarding upcoming Herald events which (for the most part though not so much lately) will always result in some sort of participation reward assuming Herald IMMs aren't feeling apathetic.

So usually there is something going on. But no matter what cabal you're in, you can set up your own quests or events and usually if the IMMs aren't busy they will pitch in. For example as a Nexun you could pray for Twist and ask for his help to set up an in cabal contest where the person who finds the most 'magical' items gets some sort of reward of his choosing, you schedule a time and date with him, and send a note to the cabal. This generates knowledge on where to find items to tip the veil towards magic and lets everyone see and discuss where the items are from after, so he'd more than likely heavily approve. I've found that the best way to guarantee people will show up is to let IMMs divvy rewards and you just do the footwork, and mention in the invite that its IMM rewarded. Folks will come for expee and edges all day.