My thousand page American edition (1854) of Liddell & Scott is sometimes useful on occasions such as this as I find it more informative than my BDB or Thayer editions. I cannot give a link as there is no copy of this edition online.
The entry for νεφαλιος gives :
without wine; wineless
which appears to be (from further entries regarding liquids) simply a matter of composition. The word is documented in regard to beverages containing milk and honey and not containing wine.
Liddel & Scott also record νεφαλιοτες as 'to make a libation without wine'.
The words seem to come, originally, from νεφελε, a cloud. And the more unusual word νεφο which appears only once in scripture 'cloud of witnesses'.
Perhaps the underlying concept is of something that is light and clear and heavenly and mobile and produces life-giving moisture.
Rather than something that is dulled and heavy and immobile and unproductive of life and produces no 'moisture' of spirit.
It seems to me that these comparisons equate with the comparison of sobriety and lack of sobriety.
The translations conveying 'vigilance' 'temperance' and 'sober-mindedness' are not, necessarily, I believe, referring - immediately - to the over-indulgence of alcohol. It seems to me that it is a matter of the state of mind that is in view.
What is encouraged by such scriptural texts, in my view, is a clear head, a sensible attitude, a reasonable state of mind. Clarity, restraint, sober-mindedness. People are encouraged to be sensible, reasonable, modest, in control.