Now there is a very easy way to install plugins: go to edit> prefs> plugins and click 'add plugin' button. plugin will be installed into writable appdata folder rather than into write-protected musicbee\plugins folder.
I think now its very easy to make so that 'uninstall' button can completely uninstall plugin including removal all plugin .dll's/resources initially included in plugin zip package. then all installation/uninstallation instructions for users will become very transparent even for dummies.
similar wish for skins.