Indeed, this is an area that has been sorely lacking. There needs to be many more events and mechanics.
I was just reading Bernard Cornwell's book, and it got me thinking about a possible religious event. Basically, a landed priest with high intrigue can ask for some fund from you, maybe 100gc, to go "in search of a holy relic." After a while, he "finds" it and house the relic at his church. People, including nobles, from around the region goes on pilgrimage to worship this relic and making offerings. Some of that offering end up in your coffer. It might even give your army a morale boost! However, if you got on the wrong side of the pope, he might call your relic a fraud and you would lose universal respect of all catholics!
There are so much possibilities for event chains with unpredictable outcomes. We need to be given reason to want to interact rather than just control our liege/vassals.
Also, am I the only one who thinks church holdings should be buffed so it is as useful as cities/castles?
http://forum.paradoxplaza.com/forum/showthread.php?818017-Vassal-Churches-are-Under-powered