Google plus is still not fully at its momentum. Maybe in a few years?
Today being present means for sure exploiting its SEO potentiality and be at the forefront in your social media strategy.
It is important to have Google+ presence, first because it is Google, and you highly need to play game, second beeing an early adopter today, will bring you more +1s tomorrow.
As your community grows and becomes more loyal, you might also see more users sharing your content.
Learn more in this interesting blog post,