As Micros suggests, I think it depends on your spec. If you're feral there's really no reason I can think of not to farm in a combo of your tanking/DPS gear. Maybe you're a little overdressed in your purples but since you say repairs aren't a big deal I would think that would just make things quicker for you.
If you're Resto: Take up gathering professions, seriously. Not worth putting together a set for your already weak Feral damage to farm Primals when Herbs and Ore are great money, and takes advantage of a Resto's ability to just ignore 5-6 monsters hitting them at once to get to them and away from them.
I picked up a few pieces of cheap fire resistance gear for farming fire motes, just so I'd have less downtime from healing. It helps, and it's only 3 extra things to carry.
I always farm in my Max DPS gear so I kill things quicker. Using the Pounce, Mangle, Shred, Shred opener, I don't take much damage when farming mobs so the increased speed of farming more than off-sets the greater cost of repairing epics.