Totally agree with Rich @rich-brooks. Your blog gives you a long-term, “googleable” presence on the web. Google+ gives you a short-term opportunity to engage in discussions, but it’s more of a “here today, gone tomorrow” sort of thing.
Google, while a wonderful and inventive company, does a lot of “testing” of various products, and then retires them after a couple of years, or when they under-perform, whichever comes first.
I’d stick with the platform that I can own. And that’s a blog.