I would say two things count among the Greatly Underated elements of clothing modelling. First and foremost is UVmapping. If you've got a nice mesh but a stinky UVmap, then it is never gonna look its best. Second is drapery folds -- that, and the tricksy "shrink wrap" method, both make a dynamic cloth engine (such as the one within Poser5+) a useful adjunct to a clothing modeller's suite.