Disclaimer: The author of this post may or may not be known for making farming pacts with guildmates ("I'll reset and re-run this instance with you until raid time every evening until you get your drop if you'll do the same for me once we get yours!") and is therefore disqualified from making rational judgments on reasonable replay value for any instance.
But surely there's more to replaying dungeons than grinding out points and shinies and rep, so let's turn our thinking away from loot for a moment. Don't use where your loot drops as a consideration. Which Mists dungeon or scenario are you most pleased to see pop up on your loading screen? What's the attraction? Is it the scenery, the encounter design, the story, or something else that keeps you coming back for more?