I don't think there is anything more boring in the game (or life in general) atm than leveling through legacy content.. The first time you do it might be alright but after the 10th max level character it just becomes mind numbingly boring. On the other hand many people, me included, enjoy playing multiple toons at max level. I just don't see why leveling has to be so slow after all those years.
My suggestion would be something among those lines. An achievement very hard to complete (something like completing EVERY quest available or explore every part of the world,or have 10 characters max level, or get some major reputations to exalted etc. anything that proves you have played the game to the max) which would reward a non-consumable BoA +300% elixir for faster levelling. I know I will probably get flamed to death by many vanilla-lovers but sorry guys, levelling is just crap at the moment, takes forever and doesn't feel rewarding enough. It's just trivial.