Take all the quests/raids in the game that have the lowest attendance, add 10% XP. Rinse and repeat until you have a better balance across the game.
This would also help a LOT with burnout, I for one, get tired of running the same quests over and over, but if I deviate, it takes twice as long to level. Also some of these quests are great and took a long time to create, wouldn't it be nice if more than 2 people a week did them?
Give a bonus to players that spend extra time in a quest. Reward the people who take the time to enjoy the trip rather than try to get to the end ASAP. It shouldn't be too hard to make a baseline and then give a bonus based on if you were over that time. NOTE: I am a zerger and just want to get back to cap ASAP, but I want to see the role-players get rewarded for playing the game the way it was designed.
If you knew that the extra time you spent in coalescence chamber or proof is in the poison and such was going to add up to an extra 50% XP for a "smelling the flowers" bonus or what ever, wouldn't you do them?
Also it would encourage the zergers to slow down when they have non zergers in the group, lend a helping hand to teach rather than tell them to just wait for you to finish it for them.
Make it easy to see by adding it as an optional, the "smelling the flowers option"
Add a bonus for non hireling group size, it wouldn't have to be much, 5% per member added, so 25% max for a full group?. This would encourage grouping and that may lead to making friends and that may lead to more time playing the game.
Any other ideas?
Oh wait! I just got a great self serving idea! Give an Otto's box or some other significant reward for the ideas your players come up with that you use!