Ok, the way to make crusades fun is to first, dedicate one place to producing priests. Make one every turn if you have too. The goal is to dominate the college of Cardinals and always get your guy elected. This gets easy once you get Master Theologians Guilds. Next, build churches, and abbeys. Next, don't actively attack other Catholic factions, at least one AI nation will be aggressive and get excommunicated in every game. If it's someone near you, which it probably will be, then make sure YOU pick every crusade target, check every turn for the soonest opportunity. Controlling the attention and fervor of the Catholic world is the same as controlling the world itself. Then while on the crusade, make all your units crusade units because they don't take upkeep when on crusade. This makes you piles and piles of money. You'll have to take it kind of quickly or stuff will start to desert but it's well worth it. Also you can make another army to take something else along the way. Plus when you take the city that is the crusade target, sack it and get even more money. You get experience for all those units whether they did anything or not, and you can keep the city if it is in a good position, or destroy all the buildings, and give it to an ally. Or a muslim faction so you can repeatedly send crusades to it, or just have your enemies be distracted by calling countless crusades on a worthless target that you have already ransacked.