A strategy that will work much better for spammers (and I guarantee that you'll see it in action) is temporary identity theft:

    1) spammer picks someone popular, signs-up with 
       similar name + similar picture
    2) spammer starts following the same people and 
       some of those people will follow back
    3) spammer starts spamming
    4) Google notices and bans account after some time
    5) repeat from step 1

Also, there are plenty of spammers on G+ already. Twitter is much more aggressive in dealing with spammers.