In my opinion Google+ will always be around and as its Google's own property it will remain important to keep included in the list of your SEO strategies. Maintaining the page isn't hard if you are already doing posts on other channels, it follows similar guidelines to Facebook. You need to gain followers by building circles, but as Marty mentioned it cant be done with advertising at the moment so will take some time doing some outreach, join industry communities, follow others in your niche, optimise your profile etc
Having a verified Google Plus page, and Google Places page correctly setup and optimised for your brand name with the right citations is also advantages in local search, as when done correctly, your Google Map will show up on the right, with reviews of your business underneath, which can help you dominate more of the page.
