They have been reducing the price items sell for on the AH if they are too easy to get, to keep the market from being flooded with gil. They're not going to increase the price that NPCs buy monster drops for in that light. Look at Wisteria Lumber recently getting dropped from 6000 NPC price to 600 gil, because too many people were farming the Goobues for that drop and just selling it to NPCs. Sparks seems to be the only currency they've been happy with the conversion rate to gil, after nerfing Chocobo Blinkers that you could buy with cruor and sell for gil.