Wouldn't the difficult per block rise, making it the same current usage as before?

The difficulty rises with the total hashrate across all miners, not on the individual hashrate/efficiency of any particular miner - if you can eke out a temporary efficiency advantage over everybody else, you can profit nicely while they're trying to catch up.

Eventually. But newer hardware will tend to be the most efficient component of the hashrate and push out older hardware by generating more hashes per unit of electricity (hence the CPU->GPU->ASIC progression).

That doesn't mean anything.

Bitcoin network bandwidth remains the same, and energy usage has continued to increase in a race to the bottom in terms of work and waste for bitcoin mining - this is by design of how Satoshi's difficulty algorithm reduces efficiency with increase in hash rates.