The purpose of gear is armour.
That doesn't mean it's impossible, or implausible, to make decorative only slots. Achaea does it. I know, apples and oranges.
But in Achaea you have two armour slots. An actual armour(body) and a shield. Not everyone can use a shield. Armour is divided up by class, for instance monks get leather armour(the weakest) while Knight classes get Fieldplate and fullplate(relatively identical pieces, just the latter is more expensive to make, never decays, and can have its appearance customized), which have the highest physical defenses.
Nothing outright offers resistance to magic, you need enchantments for that--which come on rings, of which, everyone can wear 10 of them(I think, maybe it's 8 [edit: stupid smilies >.>]). And active enchantments don't stack, so at most you can have one instance of fire resistance, cold resistance, lightning resistance, and general magic resistance. Outside of that, they're just decorative. They don't add anything passively, nor do necklaces, or gloves, or boots(boots can be enchanted to let you walk on water). Likewise there's clothing and cloaks and etc etc etc and none of it offers any defence.
So entirely cosmetic pieces are entirely possible.
But I think we do have too many armour slots(and having more armour slots -does- give people an advantage in resistances when it comes down to customs. Dragons have two slots over most races with tail and wing, which adds another -100 possible resistance, for instance)