I have found the name of the item can be a big incentive for the amount it's sold for. Sold one recently (just 1 prestige) for over 100 (on the Colonies...)
I love unique items but it does seem as if the majority of them are bought with the intention of keeping them until they are useless, then go an buy another one.
Don't let adventurers get any of the bonuses from the item and don't have them decay in their possession and I think that could make a difference to people wanting to make the effort to keep them more.
