You make a good point about the relative fluctuation of value, but if this isn't tied to a tangible the whole system collapses. And while a newton or watt-hour might fluctuate based on all the constraints you've listed its still far more relevant than something like gold. Unless someone comes out with a cheap and easy way to make infinite energy, that is. That said, I'm a fan of dragonfly.

Why does everything have to be time dependent with you? Why can't you live in the 'moment'. :)

Why not use what it all comes down to in the end? Watts. Secondary benefits would be that there would be a huge push to make transferring and storing more efficient and people would actually be able to correlate what they're buying with the cost.