I've found out that casting Identify (by the vendor) on the Green Elven Chain or Lareth's armor has no effect on their stats? Does it really have no effect, or just no effect listed? All I saw is increase in sell price. Are there other items that can be identified, but don't get any different when identified?
Identifying a magic item has no effect on its stats whatsoever. You can usually deduce the effect of a magic item by checking ability scores, skills, AC, HP, saving throws and attack bonus. The identify spell will only confirm what you already deduced, and raise the selling price, because you now know what your selling. The only items that you can't use to their full effect without identifying them first, are items that have special effects that you can choose from the radial menu (except potions, which can be used without knowing what they are). You cannot use a spell scroll, items such as the Fungus Figurine, Boots of Speed etc.