From my past experiences, it may be still viable for us to do the collection quests.

It was bad for me to do the collection quests in the Shimmering Flats. But it would be much easier / happier if you assign each character to do an unique one. For example, char A do the collection of scorpion's stuff, char B do the collection of turtle scales etc... It should theoretically make all your character advancing at the same speed.

I kind of took this approach after I left the stupid Shimmering Flats area. inch:
*Hint* some STV quests, some Badland quests...