If you remove “visitor” and use “member”, how will I (as a new user) know the difference for no username/password (casual viewer) or with username/password (registered) required to use a feature?
Same as now, surely. This is what casual viewers see at your Royals site:

The casual viewer has to read your message about not needing a user name/password. Also, there is no link shown to request a user name and password on the login block.
Changing settings from “show to visitors” to “show to members” will not change anything there. BOTH of those settings (now) only apply to people who are logged in.