Well, Improved robes of the Old Order just gives you +2 to AC and something like 5/+1 soak damage. 5/+1 soak damage doesn't do much if you're facing tough opponents, and is completely pointless against anyone with magical weapons and/or elemental damaging ones.
Speaking of Robes of the Dark Moon with the Haste effect; I once tried a Dwarven Lv. 40 Monk with those robes. Boy, could he move those little legs of his.
