Personally I'll likely get the game at release and pay for the DLC later. Of course I have Live whereas you say you don't. In which case I'd recommend getting the game and trading it in when the GotY/Legendary edition hits shelves. That way you'll have played the game and still be able to get the Game+DLC at a later time and with a little money taken off.
Mind you it won't be a HUGE discount off but it'll be better than full price for what is essentially re-buying a game with some extra bells and whistles. (All that assuming you visit GameStop at all)