The score I was looking at was Williamson Music’s Vocal Score for “Carousel”. I have a ton of Broadway Vocal Scores here and the reason I keep returning to this one is that it is far and away the best of any of them in terms of quality. All vocal scores are idiosyncratic and rule breakers - as you’d expect from scores trying to cram in as much in as possible, but this one is arguably the least so. It allows the music to breathe - there doesn’t appear to be any intention to minimise the total number of pages - and unusually (and regularly), it contains separate staves for instrumental parts.
Here’s the section I was studying. Interestingly, this occurs on a page when there was more than enough room for them to do what you suggest (i.e. ample room between sections)
Looking through the rest of the score, it appears to adhere to the principle you outline. I can’t find an example of voice 1 of the treble stave that doesn’t. But when voice 2 vies for space with voice 1 in the bass clef, rather than make a significant expansion to the space between the staves in a Grand Stave (imagine the impact of doing it in the example I’ve just posted), they do it differently.