possible to enable "gumdrop" buttons (close/minimize/zoom) in all windows (disable auto-hide of these buttons for non active window)?

I often want to use these on non-active windows and of course they're not visible until you hover over them or activate the window, which prevents instant tracking of their location. I don't think they would be distracting if they were visible on all windows, and I have a feeling there is some tweak somewhere that would disable the auto-hide feature. Has anyone ever done this?

No, what you're asking for is not possible. There's no "tweak" to remove the "auto hide feature" because it's not a feature; it's a design element of macOS.

Apple provides very specific guidance when working with the Title Bar within the Frame in their guidelines in Window Anatomy of their Human Interface Guidelines for macOS:

This is how users interact with the system and specifically, this is how they know what window is active or not. Apple goes out of their way to document how users should interact with every element; their not going to supply a way to circumvent it. For context, this can't be done in any OS GUI that I can think of ranging from Windows to GNOME, KDE, XFCE, etc. There's no reason for Apple to deviate from this standard.