I think 90-100% is a bit high. Getting chapel can't be that bad. Late chapels run into the problem that they can't really trash 4 cards, since they get drawn with something good, but even trashing 2-3 cards can be good enough sometimes.
You'll get your first familiar later, but chapel trimming can let you play your fewer familiars more, and you shouldn't lose the curse split that badly. Then once that phase is over, you'll have a trimmer deck to transition into something, and less negative points if you manage to trash curses.
I think the decision should depend on what the transition is. If it's just money, it's probably not worth it, but if you can make a rabble chain or something, you should probably go for the chapel, I think...