You cannot wear your max AC armor all the time. There are many times in the higher end of this game when you MUST wear resist gear to survive. So any items that can contribute to your WIS when you have to trade off some AC helps. I have the Ancient Tarnished Gauntlets in the bank. I have not bothered to complete the quest, and doubt that I will, simply because I have the Coldain gloves. The 4AC difference is not that big a deal. The extra WIS can be.
Temple of Veeshan mobs, fights against many of the dragons in the game, etc are all examples of times when you must have high resistances up or die.
On the other hand, if you are going to go play with the wimpy mobs in Sebilis, or Karnors Castle, then you want all the AC you can get. Take a shaman with 1100 AC into those zones, and most of the time, the mobs will miss about as much as they hit, and they will hit for far less than they would some shaman with 750 AC.