Isn't that one of the reason you started this thread? If you had space in your retainer why then complain about paying for extra storage?
Unless your a collector then yeah I can understand your space problem but how is people having more retainers giving them a edge over you? Just level 1 type of Class I.E Tank class then get rid of all your tanking gear or Melee DPS class. It's how I do, I've got 2 retainers and most of them are full of stuff I don't need.