Likes and plus ones are a game by-in-large but have you looked at the Search Engine Optimization section of Google Analytics lately?
There’s an entire section that measures traffic coming in from “Social” and that “Social” is very broad ranging from Disqus to Linkedin to of course, G+.
What is being reported and measured is traffic that engages by clicking through the social media curtain to your website. That is a challenge most people don’t like and don’t want to take on, but the rewards I have found to be high for that very reason.
If you’ve seen my SEO experiment on Google Plus, Most of what I have done has involved attracting people to visit the website. Social isn’t the end all but ignore it at your peril. It’s a strong signal when people are actually finding value in what you offer.