Okay it is clear some people are missing some info about unique's.
Firstly there is a maximum that can exist on any island at one time, I would be surprised to find that any island had more then 100 items.
Sorry, I was misinformed.
Secondly they have a MASSIVE variance in quality already. They have a differences in how much prestige they grant, if they grant a boost to a skill, how much they boost a skill and how long they can go without repair. There are items out there that last more then a few months before needing repair. The thing is as unique's age and get repaired, their duration is reduced. Sages seem unable to return them to their full potential so the longer a item is held on to, the shorter the period it can go for without repair. Still is should be possible to hold on to an item for several years.
There's a variance, but it's basically two-tiered. There's the items worth having (and even then, only barely), and there are the items that are total crap. I would never contemplate going through all the loops and uncertainties and micromanagement needed to maintain an item if it wasn't fantastic.
Items are already lost in battles, and yes can already be found by advies. Items are created by sages and monster/undead hunts, but the chance is random and is also limited by the island item limit.
I know, but I think this would address the issue of item turnover in a system where items have 0 decay.
I don't know about anyone else but currently Unique's seem like a GIANT status symbol. Since they are apparently so difficult to maintain anyone that has them is obviously powerful and well contected 
They don't represent someone's prestige or worth or wealth or connections or stature. What they do represent is someone's capacity to put up with constant annoyances.
