Spammers didn't typically scan the phone book and use automated bots to email all the people in it. So although phone books were "databases" they weren't easily accessible with some scripting.
The OP may believe that the Google+ "SPAMagedon" isn't coming - however - I have noticed that, over the last week, I have been added to the "circles" of well over one hundred "accounts". When I click on these, most of them are marketing accounts or sock puppets. Some of the names are clearly marketing: "Angry Birds Lösung 3 Stars Games.J500", "Anime TV and Title Loans Chicago", "Fred's Best Title Loans", etc. Others, when you go look at them, are pretty clearly similar. 10 people have them in circles but they have 5,000+ circled. The posts (if there are any) are just advertisements. Does anybody really think that this was random? I am pretty sure these folks are getting ready to spam using G+. Sure, they will eventually get shut down. But I'd advise people to go change the setting in GMail that allows these folks to send you mail without knowing your gmail account.