> One thing that working on the project helped demonstrate for me is that adding parens around _every_ subexpression is _way_ too noisy. But for me, I prefer drawing that line on the noisier side.

I prefer the noisier side as well. When adding parens to indicate/force precedence, I will sometimes split my expressions into multiple lines, with indentation, as an aid to legibility, e.g. instead of ( ( a + b ) / ( ( c - d ) / e ) ) I might write:

  (
    ( a + b )
      /
    (
      ( c - d )
        /
      e
    )
  )

I've found this not only quite legible, but also fairly easy to edit because you can easily match parens visually.