v5.6 out already

Simple enough: Go to ⌘, "Settings..." and untick the rules you never use. They will be hidden.

If you hide a rule which is still used in a SmartPlaylist, you will still see it when you use ⌘, "Show only active rules".

With the next release (v5.7) you will also be able to configure what you want to see in the MusicBrowser "Genres➤Composers➤Groupings➤Artists➤Albums➤Titles", e.g. to make just "Genres➤Artists➤Albums➤Titles"