I would participate. It is not too hard to be highest contributor if you loose enough man and just keep sieging. Just arrive a few month in when the other participants already arrived and decimated some to the enemies. Always keep an eye on your contribution rank. if not first place, keep sieging and fight smaller enemy armies. Split up your armies (make sure you lead one of them and if you have an heir, he should lead the other one). You will get a nice big cash price (somewhere around 400 or 500 gold, it depends) and can put a kin of the throne of whatever you fight for (Kingdom of Jerusalem?). Also, I usually take a lot of prisoners of which a lot of them can be ransomed for good cash or executed for dread (that can make people at home to leave factions). If you and maybe also you heir are leading armies, you both get the crusader trait, and you get a lot of piety as well (a lot of money from the holy father down the road). Usually all this pays of for the disruption.