I can't help but think of the Aether as being akin to the Lifestream from FFVII. Some people in Eorzea also refer to it as such, so maybe it functions in much the same way. In VII, people's souls return to the lifestream and turn into another life form somewhere else down the line. In that sense it was a metaphysical thing. But, we know that the Lifestream also had a physical manifestation, which was evidenced when Cloud fell into the lifestream and also Shinra pumping the lifestream out to use as energy (Mako). If Aether and Lifestream/Mako are analogous, then perhaps it behaves in the same way. It is a spiritual/metaphysical font of energy that courses throughout the planet, but also has a physical manifestation that can be tapped and used as energy. Crystalized Aether then would be like VII's materia, condensed, concentrated Mako energy.

Of course....if it is radioactive and functions like that.....are we equipping ourselves with the equivalent of uranium and plutonium? O.o