Regarding Dark Elf drops...
I purchased one extra (there is one free for completion of part III), thinking they will drop rare materials needed to complete the storyline, unfortunately, all I've got from ten collections were 100 coins, a combination of wood/living wood /glimmer dust, and a single earth wisp. Nothing related to the storyline. A bit of disappointment, I thought 300 gems and 22 hrs timer will give something more valuable.