I gave them some random PvP and dungeon gear from 3.0 and 3.1, then they added i200 AF gear to centurio vendor, gave them it and never bothered with upgrades after that. What's the point? Quick venture has a low requirement for "rare" stuff (even level 1 gear can).
All I do now with retainers is dress them up in an outfit and place them in my garden, sometimes even change their features with fantasia. This is literally all they are good for now.
