I do not like fixed purity maps. They divide the map into "best", "good" and "bad" spots on top of the division which we already have through biomes. The result is a sort of complex "king of the hill", where only one faction can be the "king" per server. multiple spots would encourage more concurrency on a map especially when the number of "best" spots would be too big to control for one faction.
What would help a lot - without changing the present system - would be an alchemical tool which swaps two elemental values of the item put inside. This would reduce the "king of the hill" problem to one where you would need to find only stuff with one arbitrary elemental value as high as possible.