... two different meanings of value ... "importance", which is multidimensional for all truly valuable things and irreducible to a single index, and "amount of money required to buy", where by definition the "market value" is in terms of whatever functions as money for the market in question.

Adopting energy units as a commodity-money would lead under current circumstances to a constantly deflating monetary unit, which would be destabilizing precisely in those periods of real resource constraints when financial side instability would be particularly unwelcome. They would be far more useful as an asset than as a form of money.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.