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I see what you want and agree it would be the easiest, but you could make a "Business" group for example, and add those who want to "advertise" their details to the world to that group. Then adjust permissions for that field. Those who don't want to put an entry in to a certain field don't have to it will just be blank. You could make multiple Groups, yes, more time consuming but would give you great control.
You can add members to more than one group still, well I think you can, make fields visible to only certain groups and searchable only by certain groups. You would have to make a plan on paper first though lol, could get confusing.
;o)