If you really want the players to populate also the lower level areas you should change all resource nodes to random nodes. For example when you mine metals with level 80 charr and orichalcum mining pick you have 0,2% change of getting orichalcum and 20% change to get copper etc. On the other hand when you mine the same node with level 4 sylvari and copper pick you have 100% change to get copper and thats it.