What was the extent of Christianization (or, rather, Catholicization) in Christian Outremer? Did much of the peasantry or even merchant class convert, or did Western Catholicism not really spread beyond the invaders themselves?
Uhh, the coastal cities were Catholic for nearly two centuries. That's not enough to completely destroy local minorities, to be sure, but it's still quite long; especially as this was (as you note) the focus for much of the Italian immigration, I'd think cities like Acre were quite a lot more catholic by 1291 than they were in 1099. Of course all I have is 'it seems logical' so...In short, the Latin rule made barely a dent in the religious and cultural panorama of the region - specially in Jerusalem and Edessa - excepting perhaps in the coastal cities that received a larger share of "immigration" and foreign interest, mainly from the Italian merchants, and even this had a negligible impact due to the relatively short timespan of the Frankish rule.