I have watched the Webmaster Central 2013-11-18 hangout that is now on YouTube. According to John Mueller, a site will benefit in terms of SEO if it will be optimized for mobile devices. He said that in order to do this the webmaster needs to follow the Webmaster Guidelines for mobile websites.
However John answered to this recent question in a completely different way. He stated that only common configuration errors are taken into account.
According to the "Building Smartphone-Optimized Websites" guidelines, it's recommended for websites to be responsive:
"i.e. sites that serve all devices on the same set of URLs, with each URL serving the same HTML to all devices and using just CSS to change how the page is rendered on the device. This is Google's recommended configuration."
1) Is it true that only common errors are taken into account for SERP, or it was true at the time of that question?
2) I have a website that gives the same URL, same HTML and same CSS to all the kind of devices. There are absolutely nor rules that display the site in a different way to mobile. If I open my site on an iPhone for example, I see the website displayed full screen, and the users have to tap and zoom in order to read it. This means that my site provides the same HTML, CSS, and URL to ALL the devices, but it's not responsive because it does not adapt to mobile browsers. For example a responsive website for smaller screens might have a different navbar, the sidebar goes to the bottom automatically, etc...
I would like to know whether it is advisable (specific to ranking benefits) to edit the theme of my website to make it responsive, for example using a framework like Bootstrap or Foundation, or just adding media specific CSS. Or maybe I can avoid making the website responsive because it's already fine as it is, since the same URL, CSS, and HTML are given to all devices, thus switching to responsive design will not affect my site's rankings at all?