Sgt_Kickaxe - 11:16 pm on Sep 27, 2012 (gmt 0)
The latest Google rater guidelines suggest that raters search for signs of authorship including phone number, address, an about page etc. It doesn't mention G+ but one could surmise that it would qualify on the list too.
The rater handbook also says that some types of sites (health, finance..) require more information that validates the professional status of the author (not the site owner since some owners outsource writing).
Do you NEED G+? nope, but it can't hurt in some niches.