not likely something you'll want to change for this game, but something to consider if you do another game in the future:
the various elements don't really do anything...I end up always hitting "buy all" on the auras page, and the difference in forging costs are nearly negligible.
I'm never going to look at a tree and see that it has a particular resistance therefore choose to boost that aura because it is likely going to be a different resistance the instant it ticks over to the next tree.