I just finished off all my DoH classes with only 2 retainers. Each one at any given time has around 150-160 items, with a full list for sale at all times in the market. I usually have around 3 of my inventory pages full. Now that I leveled them all also frees up some armory space. Once I start leveling other DoW or DoM classes may become tight, so to me its not worth it or needed.