Buying a used Moog Etherwave on Ebay?

So appreciative of all the advice and information! Very helpful community. I look forward to posting more once I get up and running with my new instrument. ;-) 

"...or that bendable pitch-wire/aluminium-foil pre-grounding..thing in the EW is for something similar."  - xtheremin8

Yes, it's a small ~variable capacitor from antenna to ground.  Had me scratching my head when I first saw it, and for a long time afterward, and some even now.

It clearly adds to the environmental C seen by the antenna, and so lowers the EQ coil | antenna LC resonant point, which is one of the three LC resonances on the pitch side:

1. EQ L & antenna C

2. Variable oscillator tank LC

3. Fixed oscillator tank LC

Since resonances 1 & 2 interfere (to linearize near-field pitch) I assume the wire is there to fine-tune that interaction.  Bob M. obviously experimented with the EQ coil count, so it could be the dregs of that experimentation, or design "insurance" - a way to bring a unit on the edge of out-of-tolerance, or tuning range, back in.  I believe Thierry commented on it it a while back.  I'm a bit of a hack when it comes to tuning the EW, and have never found a use for the wire.  I'll be adding an ESPE01 to a Big Briar unit soon (pretty much an EW with somewhat different PCB layout) and will do some tuning experiments along these lines.  Tiny amounts of C added to the antenna can throw tuning way off (which is why I advocate for an explicit, user adjustable C here).

That question can IMNSHFO be brought down to production costs. There are two elementary premises: 1.) the EQ coil - Antenna C resonance must always be slightly lower than the VPO free run resonance. 2.) EQ coil linearization works the better, the lower the static antenna C is (because the Hand capacitance will become more important in comparison, and thus you reach earlier the asymptotic range of the curve).

Lowering the EQ/Antenna resonance can be done in 2 ways: increasing L (expensive) or increasing C (cheap). Bob Moog decided for the cheaper way, added that foil and started shipping the instruments willingly without optimal tuning, the pitch range limited to 2 1/2 to 3 octaves above middle C, so that the not optimal linearization would not be perceived by the player.

If you tune the Etherwave to play up to 4+ octaves above middle C, you find that this 4th octave will always be compressed. This can be improved by bending the wire away from the foil, or even by partly removing the foil before you do a still more meticulous fine tuning of the VPO to bring the resonances closer. I once removed the foil completely and added a 5mH inductor just to see what would happen. And I managed to stretch this fourth octave to 90% of the octave below. But, due to other design factors, I had side effects like a decreasing oscillator amplitude (and thus an ugly timbre) due to the more important load by the series circuit with close resonance and some situations where the pitch frequency jumped over to the second pole (parallel becoming inductive and series behaving capacitive) which gave a steady ultra-high pitch of about 14kHz. Thus, to stretch this highest octave correctly, you’d need at the same time more robust oscillators like in the EPro, where all this is not an issue.

On the E-Standard/Plus, you’ll have to live without or with a compressed fourth octave above middle C.

"...one of the three LC resonances on the pitch side: 1. EQ L & antenna C 2. Variable oscillator tank LC 3." dewster 

Is relevant resonance not 1. (EQ L + variable oscillator tank L) & C (resulting from antenna, stray, self)?

"Is relevant resonance not 1. (EQ L + variable oscillator tank L) & C (resulting from antenna, stray, self)?"  - JPascal

For the C I agree.  For the L I don't think it's quite as simple as adding the inductances as there are capacitors involved.  High Q series and parallel LCs tuned to almost the same resonant frequency, and connected together.