The problem with this is you'd have to alter the whole item store price scheme & trade item price perception. If you're going to reduce the gold gotten from monsters then the prices at the store need to be changed as well: 300 gold for amulet of life, 195 for ceder crossbow, 100 for great helm, 2700 for kwarazami (whatever the hell it's called) magic sword. These are all way over-priced.
I'm fine with making such changes. I don't do monster farming so the few playthroughs of the game I've had so far left me going "How in the Hell am I supposed to afford this stuff?" But the prices are out of whack anyway.
Add an oak spear to a peasant. Cost: 10 gold 3 material Trade Store Price: 52G
Add a war staff to a peasant. cost: 12 gold 1 material Trade Store Price: 45G
Assuming there's a 30% markup for the store that leaves production costs at roughly 36.4G for the spear and 31.5G for the staff. If you subtract the gold costs of production to get the material costs (in gold equivalent), you get 26.4G for the spear and 19.5G for the staff. So the spear's equivalent material cost increased by only 35% even though the raw inputs increased by 200%. That implies some sort of economy of scale in materials manufacturing. How well does the rest of the game's pricing adhere to a consistent cost curve? I have no idea, and I doubt anyone else does either, including the developers.
Hell, why does it take 10 gold and no materials to build a Hut but 50 materials and no gold to build the MINT of Ruvenna?
Frankly, I don't really see a need to rationalize a fantasy type game' economic system; you can rationalize that the skin of troll or giant spider venom is "worth its weight in gold" hence justifying the large loot/booty gotten from "monster harvesting".
I got my Bachelor's in Economics so rationalizing the economic system is kinda a given for me. 
If troll skins and spider venom have useful properties in this RPG-seeped game we have here why can't we utilize them, perhaps for making or modifying equipment, instead of having them auto-converted in gold?
Dragon Age: Origins, as an example, has potion-making and limited armor-crafting, giving some actual reason to hunt certain monsters.
My experience has been this: all that additonal cash I get from "monster harvesting" just gets spent outfitting champions. You can spend 2000 gold easily outfitting one single guy with all the armor, amulets, medical pack, longbow, etc
While that may slake every RPG'ers thirst for accumulating loot, it doesn't really serve much purpose because champions do so little anyway. What good does it do to spend $50,000 turning a Honda Civic into a 500WHP monster if I can only use it to get my groceries, just like I did when it was stock?
