Google+ shares are nofollow and therefore it will not directly improve your rankings on the serps... It may have in the past... In addition G is fully aware of how easy it is to purchase shares from dodgy services...
Further social signals do not have a direct impact on rankings... Its a myth that still persists, despite G even stating the case.
That said there is an indirect impact whereby folks whom see your site through your social media may go off and provide backlinks on their own sites... I also suspect social signal may also corroborate link creation i.e. increase in backlinks look natural when there are social signals detected....
That aside the use of social is a great way to get traffic! It also means you diversify your business from not just relying on search traffic which is a great thing!
