I'm not sure if it'll pan out, but I personally have my eye on farming the BC dungeons for their sets (they're recolors of the Vanilla raid sets, and as such not as same-y as later dungeon sets), and Island Expeditions (with their plethora of different sets, often recolors of raid tiers, but you take what you can get).
Of course, I'm lucky in that back when I had game time, I did a decent amount of farming for transmog (mostly ICC and Black Temple). Male dwarf paladin is an entirely different beast than female nelf death knight, and my tastes in fashion have diverged as well, but it's more than most pure F2P's get.