The insane condition does usually not bother my party in castle Darkmoor. There is some loss of SP and some more HP, which I'm surprised that you don't approve of . It's enough to cure them once a day, or before they rest, whichever comes last. They are very careful about keeping some item that stops them from falling asleep instead. They also keep collecting items that adds SP and enhance magic skills.
Do extra resistances really make any difference? How do you test that? And "of the Phoenix"?
I do miss "harden item" in MM6. Since I hate shuffling stuff between the characters everybody ends up masters i repair .