Buffing the XP from Dungeons would have numerous benefits.

It would give players an alternative leveling option that isn't zerg based and requires more skill.
It would mean more people running the Duty Finder and thus less wait times for everyone.
It would give players more options to master their Job ina group environment instead of spamming their fastest attack ad nauseam.

FATES should have been designed to scale based on the number of people in the area and tags for FATES shouldn't be limited to the Party or player that tagged the mob. If they were more like the Rift's in Rift or the PQ's in WAR they would be much less soul crushing. IMO.