I’ve always called minification “spending dollars to save pennies”. Other than the fact that minifying CSS files make them non-human maintainable, I hold that in a well-developed site, your savings in filesize will be less than 30kb. 30kb, you can save more by optimizing images and enabling g-zip compression. I’d rather keep human maintainability for the 30kb, take the 2-point ding in pagespeed score.
Many developers work with prettified, well documented css, and then have a minified version generated automatically during the build process – it’s part of their work flow, so it doesn’t really take any effort. Plus they’ll never need to look at the minified files directly.
I can’t think of many situations where a developer would want or care that a page’s css is easily read by visitors using view source.
You can optimize images/gzip and still also minify css, html, and js files.
Even if 30kb doesn’t impact performance noticeably, it is still extra data that the user is going to have to pay for if they’re on a mobile network.