I suggest additionally to implement a demurrage fee. Demurrage gradually reduces the value of currency held: it is in effect a negative interest rate on currency in circulation. Both inflation (made by mining) and demurrage reduce the purchasing power of money held over time, but the market price should be stable:
1. price of coin should be much more correlated with energy price and GPU depreciation - 1 coin / 1 kW = const
2. demurrage, like negative incentives, makes that a currency would suffer more rapid circulation than competing forms of currency