Quote: Given unlimited precision samples a signal which has no energy above the the system nyquist is _perfectly_ re-constructable, not just "good".
I disagree with this statement. something can be reproduced, but not neccessarily _perfectly_
also, any time you have more than one frequency involved, they are going to mix in your sensor, and so you are going to have energy above this frequency.
sampling faster may not be the most efficient way to get better SNR, but it's actually much easier to sample faster than to sample with more precision.
using your example, setting something up to sample 1 bit @ 3MHz may be far cheaper than setting up something to sample 20 bits @ 48KHz. In addition, the low-precision bitstream may end up being more amenible to compression than the high precision bitstream. with something as extreme as the 1bit example, simple run-length encoding probably will gain you much more than a 3x compression ratio. That's not to say that a more sophisticated , lossy, compression algorithm couldn't do better with the 20 bit samples, but again, which is simpler?
I am in no way saying that people hear in the ultrasonic directly, However I am saying that some people listening to a 15KHz sine wave vs a 15KHz square wave will be able to hear a difference.