I'm currently using Courier Prime Code with 60% parentheses, vertically centered around the lower case "o", and moved a bit left and right to open up expressions, and for better spacing trailing )))'s after a letter. This is easily accomplished using the demo version of Glyphs Mini, and it puts focus back on the text, without interfering with tools that expect parentheses. (I used a preprocessor for years that inferred most parentheses. It can be done, but then standard editor tools for Lisp don't work.)
There are deep reasons one might prefer Scheme to Common Lisp, particularly as a mathematician. Not liking Common Lisp's default "GET OFF MY GRASS" upper case is a shallow reason. Call me shallow. It was a revelation to realize that I didn't like Lisp parentheses because they were also upper case, and they should also be lower case.