File-based tools is an interesting question. D-Bus is hierarchical, but it's also strongly typed, so you'd have to encode stuff as text, and when you get the serialization wrong, write(2) can't give you a useful error message. But maybe it'd be useful for reading and monitoring.... imagine if you could `sudo tail -f /dbus/org/freedesktop/UDisks2/Manager` or something, and see all calls to it.

I've been using D-Feet and dbus-monitor, which seem to be solid enough. D-Bus does have extensive introspection.

But yeah, in general the state of D-Bus tooling is miserable. Part of it is how verbose it is — which is fine for compiled software, but for interactive use, it really makes you miss the "creat" and "umount" school of thought. Part of it is that there aren't great introspection tools at the command line.