While I love the idea, what a lame way to implement this whole thing. Flipping a switch and making these zones better doesn't do much for my overall enjoyment of the game. I fully admit I'll use em for PLing though.
However, it took me all of 2 seconds to think of a different approach (could be better or worse, but in my opinion it's much better) that would not only feel more rewarding, but give people reasons to actually Quest. This game is called EverQuest after all.
Make the Quest give you a new Charm (get the slot used for more than the pop idol thing).
These new charms will be for the old world zones. Each one will give a boost to the XP earned in there to bring them more in line with the PoP type zones.
Could have various levels of the charm as you advance through the quests. So when someone equip's the charm and is in that particular zone, you'll get the bonus.
Could probably include Kunark and Velious zones eventually, but I would start out with just most/all the old world zones. Make the difficulty of the quests scale up as they go, so by the time you get to say a "Sebilis Charm" you'll need to do a difficult kill to finish it.
Otherwise I love the Hot Spot idea.