Should you start a Google+ page?
Almost certainly not.
How would your members hear about it? You would have to promote it through your existing channels.
Yet, if they're already listening to you on those channels, why would you want to send them somewhere else? Why would you split them up? Why dissipate your community across ever-increasing platforms.
Did your community even ask to have a Google+ page?
I've been fighting shiny objective syndrome for the better part of a decade. You can happily ignore MySpace, Facebook, FourSquare, Quora, Twitter, YouTube etc...Community members on one platform rarely demand another.
Focus on the fundamentals. Stimulating interactions, building relationships and developing a sense of community.