More precisely, it implies that it makes us (universally) no more prosperous.  Gaining efficiency over time itself costs time and energy. 

 The difficulty in this presention is that electricity consumption is a component of GDP.

Standard of Living does seem to be driven at least in part by 

Energy Consumption * Efficiency of Usage

where efficiency is a measure of energy applications' ability to increase individuals' (subjective) welfare.

If individual decisions or markets direct energy consumption toward efficient applications, energy consumption will naturally be positively correlated with standard of living. Worthy of note:

1.  In an environment of finite, diminishing energy supply, the above positive correlation will exist at each point in time -- even if everyone's standard of living is declining over time (which would be bad).

2. Diminishing energy supply might be induced by a physical constraint on the availability of energy over time. It also might result from government regulations restricting energy availability -- or even from massive destruction of infrastructure due to war or a catastrophic natural event.

My head hurts. Too old for this. 

SHSS.