If dungeon XP is even remotely close you'd see FATE xp go down because FATE xp is dependent on having a certain threshold of people, since the effort it takes to get gold on FATE is roughly constant but the amount of time to complete a FATE as well as its frequency depends on the number of people in the zone. I don't buy the whole 'doing dungeons makes people better' because I see plenty of guys who have no idea how to play in the dungeons, though it's good to have a change of pace. Even if the reward isn't better, I'd prefer to actually do something more than just spamming Scathe/Flash/whatever over and over.