Allusion, you are making yourself look bad, let me dumb down the wikipedia article for you in one sentance:
Schumann resonances occur because the space between the surface of the Earth and the conductive ionosphere acts as a closed waveguide.
Definition of a waveguide:
A waveguide is a structure which guides waves, such as electromagnetic waves or sound waves.
All that the existance of schumann resonances prove is that the ionosphere has the capability of reflection electromagnetic waves in the radio frequencies, "ELF" region, which I believe stands for extra long frequency.
THE ONLY THING THAT THIS MEANS IS THAT THERE IS THE ABILITY TO "SEE" ELF-REGION FREQUENCIES OUTSIDE OF THE STRAIGHT LINE OF RADIATION. I.E. YOU HAVE THE ABILITY TO "SEE" LIGHTNING REFLECTING OFF THE IONOSPHERE.
Spice:
Firstly, there is no actual amplification of the wave - there is only the conservation of it for a longer period of time, say relative to a higher frequency wave, due to the resonance.
Secondly, yeah, there is alot of energy in the atmosphere, but what you are talking about - the ionosphere being of charged particles creates a POTENTIAL energy, which is different than actual energy. And yes, I know there is alot of potential energy, we witness it in every rainstorm, it's called lightning.
I have ALWAYS thought of the reason why we do not harness the power of lightning (i.e. the ionosphere's potential energy), and the only reason I can come up with is there is little ways of capturing millions of volts for useful power. I'm sure each lightning strike is somewhere near the million watt mark - meaning one strike could power a small town for a few weeks. But, how to accomplish the capturing of a voltage that is so large it can create a 1-mile arc to a non-conductive surface, such as dirt?
Allusion, you are stepping out of your circle - Spice, you are argueing the wrong points. I completely agree about the electrical potential of the ionosphere, but that isn't closely related to schumann resonances.