The Wheloon and Storm Horns chains could use a further bump, save for maybe What Goes Up Epic which looks nice. I would focus a bit on the heroic versions of Wheloon/Storm Horns as the experience bumps were on the small side, and those quests give rather low experience to begin with compared to other quests of the same level (imo anyways).
The druids curse chain is kind of a disaster - in that two of the four quests are really short, and so can't really get boosted much more without becoming a new "von3"-esque farm. However, Thorn and Paw and The Druids Curse could likely stand from some attention.
Cannith challenges were brought up by the players, and could definitely benefit from attention. They are a "love or hate" type of quest, but I personally loved them. However, they are the type of quest that no one really wants to do - only "need" to do for a specific item. Which I get, but it is disappointing as I found them to be enjoyable.