"Okay, so I think the high voltage seems to play a part in providing a more useable 'pitch field' (as you put it), which translates to better control (yes?). Does the 'Q' translate to a sensitivity peak in the 'pitch field'? (assuming that makes sense), whereby low q spreads out the pitch and vice versa? Just attempting to parlay my own related knowledge in case that works. ; ) I understand the 'padding' to mean a higher ratio of capacitance within the system vs. what your body would contribute, that would explain the stability, but perhaps it means less sensitivity?" - keyman2
High Q gives you higher voltage swing with less energy input, and gives you better selectivity (noise rejection). A large voltage swamps external interferers, and the selectivity tunes more of them out. Less energy in means less heating, so less drift. It's all win. High Q is also associated with oscillator stability and accuracy - quartz crystals have crazy sky high Q. High Q gives you a massive phase gain around the LC resonance frequency, which makes the region more well defined.
C padding is often right at the antenna, which can be orders of magnitude larger than the delta hand capacitance of roughly 1pF, or the static capacitance of the antenna of roughly 10pF. Low frequency analog Theremins can possibly employ the C to give a certain playing range I suppose, but it is a voltage killer too. Beyond that I've never quite gotten why there's sometimes something like 220pF at the antenna of some Theremins. Though this is a field many seem to dabble in.
Adding parallel C at the antenna will alter the playing range in terms of what note will play when your hand is say 12" away, but it won't alter the number of octaves. This is fairly counter-intuitive, and has to do with the C response fit to the ear's log pitch response.
"That's the impression I get, the newer consumerized theremins are more 'gimmick' than professional instrument - okay if you want to make noises or limited note range, but not up to par with the etherwaves etc."
Pretty much. Kinda sad, because at this point everyone could have a fantastic Theremin for like $150 or so. There isn't that much to them. The Theremini is an OK synth with fairly shoddy C sensors, too bad it isn't the other way around.
"There was a Burns unit here a summer or two ago, but again, it seemed a compromise...."
IIRC Thierry stated the Burns uses RC oscillators. Ugh, no wonder they drift. I've looked into a lot of approaches and LC is the only way to go. Even the spread spectrum approach uses LC (with low-ish Q to work over a larger range of frequencies).