Leveling outside of instances can be ok as long as
a) you avoid collect x/y quests
b) you have no competition for a given spot
Last night i tried to level at the first furborg camp when you enter felwood (lvl 48-50) mobs with my lvl 47 group.
It was easy as hell aoeing the camps but after three pulls there were no more mobs excecpt for some lone wanderers. Since i didn't want to wait for respawn i just went back to zf.
The problem is that you can't really kill mobs that are many levels higher than your group since red mobs resist too much and there are few spots where yellow/orange non elites respawn fast enough.
I will try the wpl fields tonight and see how the respawn is.
Remember: it is all about having fun,
Bunny