I definitely have an older e-standard, but...
I think many (certainly not all, but many) thereminists regard the Rockmore custom instrument as having the definitive Theremin sound, and wish to emulate that. If you listen carefully you'll find that it had a very buzzy sound... it didn't give the impression of being buzzy because of the way Clara played it. Vibrato has a huge effect on the sound of a Theremin, because the waveform is constantly being altered by the constant change in pitch.
So, I'm just pointing out that buzzy isn't necessarily bad.
I also think it's interesting that Moog Music has continued to refine the Etherwave Standard, even though it's established technology. I doubt many instrument makers often say "we have a product that's the best selling instrument of its class, and nobody is interested in paying more for it... let's improve it and charge the same amount!"