I have autoscan off as well.
Whenever I install 3rd party instrument/fx or a PC module, I know I need to rescan to pick it up, since it's new to my system.
Never really cared that the Plug-In Manager rescan button says "Scan VST Plugins", I just knew clicking it will pick up what I just installed.
Whether a PC effect is a vst or not seems pretty moot - it's a new plugin and I just scan it.