It would depend on the item itself, really. Something like a new pvp potion could devalue currently existing potions (this applies to any new consumables). A new weapon/armour that only exists for PvP could similarly devalue current weapons /armourthat PvPers commonly purchase.
So the new item would have to be either incredibly well balanced and distanced from current content to not effect it, or have an utterly unique effect/mechanic that is completely different from existing items, so that the items don't tread on each others' toes.
I know that devaluation is really not a big deal, but it still does effect things, and so the people it may effect should have a say.
I'm aware this is a rather extreme opinion of the whole topic, so take it with a grain of salt.