old raid content. Some of the original Azeroth raid content has excellent encounters and interesting story-lines, but adding another ten levels to the game hasn't made them any more accessible to more casual players. "But Elizabeth," I hear you say, "I'm level 70 now! Surely Ragnaros, in his puny level 60 dungeon, holds no real challenge!" But that, dear readers, is where you go wrong, because raid bosses do not have set levels -- all of them have a skull displayed where their level should be, which means that their level is 3 levels above the highest level player in the instance, and that no matter how many levels are added to the game, they'll always be tough fights. While this adds some sense of realism to the world (from a lore point of view, Nefarian, son of Deathwing, should never be soloable, duoable, or even 5-man-able -- though his smaller sister Onyxia is getting there), it also means that more casual players will never be able to check out some of the game's coolest content. Any above-your-level boss requires some decent +hit gear for you to be able to touch them, and if you're geared out well enough to tumble with level 73 monsters, why not just do existing raid content?
From my perspective, the old Azeroth raid content was great fun and should be as accessible to players as possible. It's not like a level 70, even wearing only quest rewards and green drops, is going to be getting any gear upgrades from Molten Core or Blackwing Lair, so why not let them have the chance to experience the content for fun?