Some items in the game are not used by anyone I guess. I think that probably all the "rare" items are not used at all.. Some epic items are only used for those that cannot afford the legendary stuff (with a very few exceptions when higher lvl epic has exactly the same stats as the lower level legendary item but it is much cheaper).

I'm pretty sure that it was not the goal, but I might be wrong. If I'm right I guess that it can be changed by restricting usage of higher rarity items. Basically it should be done via higher market price but it does not work because most legendary items are so cheap. Mythic and arcane have lvl restriction and that is good. If you could do the same for other rarities it might fix the problem.

I have a suggestion for the possible improvement:

Could you make higher rarity items usable only for toons that has earned specific achievements (some new epic achievements based on total achievements points or quests grants usage of epic items etc.)?
Or it should be a new skill required to be able to use those? 1 point - epic, 2 points - legendary, 3 points - vanity, 4 points - mythic, 5 points - arcane ?

This is just idea and I see it is not the perfect one (I know that people used to legendary items already), but please maybe have some internal discussion on the subject if you agree that the current situation needs a change..

Anyway at least please consider to have liquidation prices dependent on item levels and rarities..