(edit)CONCLUSIONS:
- according to economical basics, energy consumption of the bitcoin network does not depend on mining gear efficiency!
- the problem described applies to every proof-of-work based currency (including Litecoin) because proof-of-work equals proof-of-energy-consumption at a market equilibrium
- bitcoin value is NOT directly backed by energy consumption. But mining rewards and transaction fees are.
- the slower the bitcoin value rises and the lower the transaction fees, the lower the energy consumption of the bitcoin network on the long run
The OP is more or less correct. As long as extra mining is profitable, more electricity will be pumped in to mine. Efficiency of mining technology isn't important for this question. The important thing is how much the annual distribution of coins are worth at the time. Electricity worth a similar (but smaller) amount will be used for mining.