Some say that the stackable Etched Acrylia Runes are Grimling currency in various denominations. For me, it might as well be currency since I trade it in at the "currency exchange" (i.e. I sell it to NPCs); I've yet to find any use for it.
The more lucrative (although less common) drop is the acrylia ore. This ore seems to be in good demand with players who practice tradeskills. One problem is that bricks and blocks cannot be stacked (as of this posting date). However, if you have good smithing skills you can do various combinations in a forge to transform the ore into more stackable forms for end use or for selling to other players at a more convenient time. For more information on smithing conversions, check EQTraders.com.