I think UO's item decay was one of the best item designs implemented to date. Everyone had gear they'd reserve only for very special occasions (Heavy Xbow of Vanquishing!).
For those unfamiliar - weapons and armour had a maximum durability, as this reduced so did an item's damage or armour properties. You could repair an item, but it lost a little of its max durability each time dependent on your skill - so eventually you'd have to replace the item altogether.
You could do something simple with Procs and Item charges to depreciate items in EQ. Otherwise you could implement some fairly simple source changes for a more elegant approach, e.g.
- add a 'condition' field to the item class (representing a % of condition)
- use 'condition' to multiply damage/ac/stats in the relevant functions
- include a chance to reduce condition in combat events
Then you can remove no-drop, and while items will be tradeable, there will be a constant flow required and people will tend to keep 'spares', and/or sell part damaged items.. restricting the flow of godlike items to the undeserving