If they overhauled the entire game, not just the new content, with state of the art graphical fidelity, more involvement in the combat and more varied quests then they'd have me back. Let us feel as though the game has a budget that speaks of it's profits, because its the fact that so much revenue is made from the game and so little is put back into it by comparison that the majority of the leavers have left.
That and the ridiculous retail price on top of the subscription model, the amount it costs you in the short term (new player) and long term(veteran) isn't the value some think it to be. For a lot of players it's like smoking, at first it's great but after a while you're just doing it from habit and to feel normal. I doubt many players get the kind of buzz outside of raids as you would from a AAA title, and raiding doesn't provide the kinda return on your investment to make it good value for money.
That's my two cents anyway.