I think a reasonable way to help alleviate the frustrations of duplicates would be to implement a way to exchange a duplicate weapon into a totem/nut within the instance. I imagine this would be complicated to do and would likely involve introducing an npc into the instance you could trade existing weapons to and let the new weapons drop to you. I'd say one to two items in exchange for a duplicate would help people out alot getting what they want without making it really easy to obtain them.