If you want to keep equipment rewards on mid-level content and still make it worth doing an appearance tab/slots is a healthy way to either keep folks comming back or atleast having them want to visit. Make Dungeon rewards themed to the dungeon, make mission rewards themed to the mission State/company/guild house etc. And have appearance slots so there is a secondary reason to run besides just stats...

Don't get me wrong, Stats are sweet, good gear is too, but honestly few people are gonna gimp them selves so completely for looks, which means there will only be a few select "worth it" things to run Mid-level range before you've either outleveled it, or will soon enought that the stats won't be worth the run.

On the reverse give those same items themes, interesting or fun skins with an appearance tab, and you give a portion of the population a secondary reason to run/do whatever. To look slick and stylish.