In my opinion the current cost of switching the nether aura trait is too high.
It costs 30 Exalted Emblems to switch the aura to a new random one. However it costs only 25 Emblems to create a new nether that might also have the aura you wish for(as a bpnus you get to keep your old nether). The only reason to currently use a “Scroll of Renewing” is if you already invested into your nether before you “fixed” its aura.
My favorite change would be to split the current “Scroll of Renewing” into five recipes, one for each aura type. Increasing the cost would be fine, for example add a cost of 100 of the *Amber material associated with that stat. The deterministic nature would explain the higher cost of the scroll.
Other possible changes would be to decrease the number of required emblems for the “Scroll of Renewing” or to (please don’t) increase the cost of creating a new nether.