You know, it occurred to me when I was adding tags to the toons post that I forgot to mention the only character I've ever transferred. Back when I was still playing mainly Alliance, I had a paladin. Said paladin even has her alchemy in the 280s. She's level 36, and has been for three years. I transferred her off Bronzebeard when it was free to free up space to roll my shaman. I've done two things with her since her transfer: get her free pony when the level for it was reduced to 30, and change her hairstyle when Duskhawk was trapped in the Stockade for two or three hours (oh, the irony) following a server crash a couple weeks ago. But you can add paladin to the list of classes-played-more-than-20-levels.
PS: She now has the same hair as my Blood Elf bank rogue. It's very cute on humans.