I have, I've actually written my own GTK theme years ago, before I gave up on it. B00merang Project's stuff is cool -- still way larger than it ought to be but indeed better -- but GTK theming is a raging dumpster fire.

Not just GTK themes but all of the tweaks and extensions that are apparently necessary to have a UI usable by an adult. Even then it's a moving target and some GNOME update will break random shit or remove some control. It's absolutely infuriating.

I find the server 2003 theme to be much more eye pleasing, mainly because it is designed to use more than 256 colors. https://github.com/B00merang-Project/Windows-Classic

While I like the overall feeling of those themes for nostalgia reasons, they've got all sorts of quirks. E.g. toolbar icons aren't correctly aligned (you can see that in the screenshot, on the "forward" and "back" buttons in the left corner) -- both the horizontal and the vertical margins are wrong. It's not the authors' fault. I've poked at GTK's CSS before -- you can't make it work, not at the current abstraction level.

Also, for comparison, a Finder sidebar item is about half the height of the (unresizable) Nautilus sidebar item in the screenshot. Thank God for Thunar at least :-).