Yes, and at equilibrium, the energy spent by the network has exactly the value of the minted coins.
Proof of Work = (literally) Proof of Energy Spent
There is no such thing as "efficient" mining hardware.
I would disagree with your statement about there being no such thing as "efficient" mining hardware. I would define efficient miners as machines that use less electricity per GHs then the network does as a whole.
Of course, mining hardware can become more efficient. The point is
that does not matter with respect to the total power and/or energy consumption of the Bitcoin network. Look at the math above where I proved this to you.
https://bitcointalk.org/index.php?topic=520977.msg7687843#msg7687843Also, if that is too much to read then re-read this until you understand it:
Your theory doesn't match the facts. People just keep adding more mining hardware until the electricity consumption is as much as they can stand. The diff rises and they get less BTC than they were getting with the lower efficiency setup.
See yet?
In theory, you could add a little bit of additional mining capacity (that is very efficient in terms of electric usage) to the network that would increase the difficulty a small amount, but that small amount would make it so a lot of less efficient miners no longer mine enough to earn a profit after electric costs so they are taken offline, and then subsequently replaced with more efficient miners with equal hashpower but with less overall electric consumption.