I was doing that for a while but with the SB level cap increase I turned in most of my dungeon gear becauae I can just go run that older content unsynced or, if I really need to, bring a friend to make sure I can clear it all. It freed up 1/4 of my retainers.
In response to the OP there is very little left to say in the way of good advice that hasn't been said. At this point if you aren't going to start crafting now I say sell off the vast majoroty of the mats. If you want to be safe do it all through the market board; this way if you go to sell something and see it's exorbitantly expensive you can make an individual decision right then and there to either keep it so you don't have to buy later or sell it and make some (basically free) gil.
