I started on the throne of Castille, but I haven't had the same success, haha. I'm loving the free upkeep on the holy orders. I always seem to use mercenaries though, and in the past 10 years I began using Holy Wars and ducal claims to expand.
I never join the crusades unless they're right next to me. The current one is in Jaffa...about 10-20 years away from Spain.