Currently value is primarily associated with scarcity. Things like breathable air and drinkable water do not become valuable until they are scarce. This is clearly a problem if we want to have values which reflect the real value of things within a living system.
Also, our models of wealth are completely upside down. Real wealth (derived from "weal" referring to wellness) is not a function of how much stuff you can accumulate. This is like thinking that becoming as fat as possible is to be healthy, or that cancer is a model for healthy systems. (Cancer uses all of its resources to grow more cancer until it kills its host.)
Real wealth is a function of how quickly people's needs are met. You only NEED a few things at a time. You don't need the car when you're not driving it, or the extra house, or the boat or the closets full of clothes you're not wearing. You just need access to those things at the time that you do. This means that scarcity should be dealt with exactly the opposite of how we currently do. Currently, scarce things become costly and hoarded by the wealthy so that even fewer people have access to them. We need currency systems which optimize effective sharing of scarce things so that they can be where they're needed precisely when they're needed.
Money does not do that.
In fact, commercial economies don't do this very well at all (although capitalists loudly exclaim that they do).
As far as I know, the most efficient models for doing this are gift economies. Things are given to who needs them most when they are needed, rather than hoarded by whoever can acquire the most and always underutilized.
To people thinking inside of traditional economic mindsets, this sounds ludicrous at first, but consider this everyday phenomena: Families. Can you imagine if all the things that are shared within families needed to be transacted through commercial exchanges. I need to use the car to run errands, so I have to negotiate a price and pay you for 45 minutes of use. You need to use my shower. You want to watch my TV. Shall we charge for square footage of foodstuffs stored in the refrigerator? Think of how much less efficient a family would be if it didn't operate on a gift economy but actually had to negotiate and process payments for every item shared.
We are one big family. We live in a big house called Earth. We share our house with all other life on the planet, and in turn it shares with us. Our whole commercial economy is built on plundering this gift economy. What does the earth charge for oil, trees and fish? What does the sun charge for growing our food?
So, our challenge lies in designing currencies that facilitate gift economies so that we can maximize the efficiency of our resources and have healthy models for wealth instead of cancerous ones.
There is no such thing as a value-neutral currency. (Yes, I'm speaking of currencies not of markets.) Every currency embodies particular values. It does this by what it measures and what it ignores. Taking care of your own child is not valued in our commercial economy. But as soon as you pay someone else to do it, it becomes a part of our GDP. It is taxed and measured. Only then does it become "valuable."
If currencies are tools for facilitating currents or flows, having one global currency would be like all organisms having one shared bloodstream. There are good reasons that human blood is different than that of fish or tree sap. Currencies can and do (even if we fail to recognize it) fill value niches to support a great diversity of living social systems.
We are witnessing the death of our industrial age economy, and all of its embedded values and financial systems. This is a good thing, because it has become a cancer that is destroying the planet, our lives, our health and itself. About 98% of daily dollar volume of financial transactions occur in the speculative markets (stocks, bonds, currency trading, futures, derivatives, insurance, etc.) rather than in the productive economy. And we think this doing us a service? And this isn't going to skew the whole system out of balance? And that the people who gamble with our money deserve to be paid 100+ times more than people who take care of our kids?
I've got a post brewing about the principles and dynamics of the new economy. I'll try to get it up here soon.