I think it should be put into considering altering the graphics on some the buildings when update, makes no sense for instance you need 200marple to upgrade a hardwood forester building, and the upgrade doesn't even show any use the marple stones you spend upgrading it, same goes to similar buildings, i have not gotten so high up yet i know the extend of this but some the obvious at my current level would be:
Hardwood Forester
Hardwood Woodcutter
Hardwood Sawmill
Feel when you do spend 100gold and 200marple which seem to be base requirement for upgrading to level 2, it should show in the graphic changes of the buildings.(that resources was actually used in the upgrading process).
EDIT: Suggestion for instance for Forester could be, making building evolve more with stone in terms of a gardener building, and wood cutter could get more a stone fence/wall around maybe the store section with more stone, also sawmill should have more marple stone added to it, if its to much work doing similar in tier version maybe make different stone color tints.