Leather and/or cloth armors should be weakest.
I think I probably agree about not having bronze or anything... doesn\'t make that much sense...
About the rituals for enchanting being long lost, how long have people been down in this cave? Is there an opportunity for that, storyline-wise? (I really haven\'t been following that stuff enough, myself...)
I personally like the idea of crafting magic arms and armor. Perhaps a more powerful set, artifacts or something, could only be found, or made by deities, or by NPCs that are themselves vastly more powerful then we\'ll ever let a character get.
Diamond armor isn\'t that great an idea, but diamond studded mail (or something similar) might work...
Oh, and gold and silver armors are protected by the Gods, because they\'re purty, or something...