The cost to change appearance shouldn't ever be free in my opinion however the game is begging for an infinite use wardrobe/makeup....stone...thing and just make it cost gems (a small amount) to change the appearance of each item instead of coins like the salvage-o-matic. Have it convert all transmutation stones to 'free uses' and voila, no one loses.
"But I don't see a point to it, just buy stones..." I hear you say. The main draw would be having saved wardrobes. Change all clothing+hair at the press of a button. Now THAT'S Fashion Wars. No doubt ANET would want to change for extra slots but hey, not going to tell them how to monetise!