Things I've noticed;
Could be way off but seems worth mentioning. Didnt do any scientific testing...
It seems like different areas yield different types of items. If you notice, if you are on a leve to get bone chips it send you to mine in a totally different place than if you are after ore. Trees in certain areas seem to follow suit, with some giving more feathers than wood bits... as i said, could be luck.
Aside from that, is there a site yet where you can go to "yellow copper ore" and it will tell you all the things it is used to make?
Lastly, is there a place where you can see where you can get different crystal types located by cities. (such as for wind crystals need Grandinia or whatever)