> doesn't mean I dislike having nice things like desktop transition effects or transparency
If you're using a DE (like Gnome) they bring it by default. If not, well, you can choice any of the multiple window compositors out there. However if you're using something lightweight enough to not bring a compositor by default, well, you probably asked for it.
Compton is a lightweight alternative BTW.
> or auto-mounting USB drives.
This isn't really a problem since systemd-logind. Just make sure that you're starting X.org in the same TTY that you logged in, or at least make sure you're using a Display Manager. After that, any File Manager that supports auto mounting will work, even without running a DE like Gnome.
Last time I setup my i3-wm workspace it was simply a matter of cloning my configuration from GitHub. Everything DBus related (including auto mounting) worked. Never more I needed to do insane things like:
$ ck-launch-session dbus-launch i3 # or it was dbus-launch ck-launch-session?