There is not, and should never be, an equivalence between something being a real currency sink and an ISK sink. The two currencies are meant to be wholly separate from each other.
The value of NPC drops is determined by the rarity of those drops and the player-driven market. It has nothing to do with the faucet aspect of bounties. Sure, you could fiddle with drop rates to change the market value of an item, but by doing that you also impact overall game balance which is a horrible idea.