There is no directly visible effect.
The buffer stage makes sure that the supply voltage for the pitch and volume tuning potentiometers is very clean so that RF artifacts (which are modulated onto the power supply rails) don't come back to the oscillators via the tuning stage, thus preventing unwanted feedback, intermodulation, ghost tones etc. In my eyes it's like taking an umbrella along, even when it doesn't rain.
A second, more obvious effect is that thanks to the combination of the 2k2 resistor and the 100uF capacitor, there is a time delay of about 200ms which can reduce most of the "pop"s and "squeek"s during the power on or off phase.
Out of that there is no influence on the sound and the playbility of the instrument.
You can easily see if you have already this circuit or not: Open your Etherwave and look near the 10pin connector which goes to the front panel. If there is a transistor Q9, an electrolytic capacitor C33, a ceramic capacitor C34 and a resistor R41, your Etherwave has this buffer stage.
If newer models perform slightly better, it's not because of this buffer stage.
It's the improved circuit board layout starting with version 211C which gives less parasitic capacitance around the linearization coils. That makes the tone spacing in the high register somewhat wider and allows a more extreme tuning up to more than 4 octaves above middle C while older circuit boards allow only to go up to somewhat more than 3 octaves and this with a smaller tone spacing. The disadvantage of the newer layout is that the pitch field is more sensitive to the environment and you can easily "overtune" the variable pitch oscillator, making the instrument first instable and then killing the oscillators' transistors due to a too high resonance current. That's why I don't stop telling people that touching L5 is strictly forbidden if they don't have the equipment to make sure that the resonance current will remain below the critical value.
