I personally do not use my lvl 40 very often unless it's on certain bosses, an area only for Legendary character's would be a great addition to the Nightmist universe. This could also add a new option for people who are on the game all alone, especially if they have an incentive, like craig previously stated, a raise in the amount of gold being dropped off the mobs. Maybe add a boss in there that will drop some weapons or crafting items that aren't as easily obtainable because of the player base, like ceramic javeliin, aetherium paragon or even maybe a rare drop of a skeleton key.