Another tidbit coming out of the Google+ hangout yesterday is that Google confirmed the mobile-friendly algorithm being released on April 21st is a yes or no / on or off factor. Either you are mobile friendly in Google's eyes or you are not, there is no level of degrees of mobile friendly.
Google's Mary said at the 47:10 mark:
Will degrees of mobile friendliness impact rankings? E.g. two sites, same SEO, both mobile friendly but one site has a better mobile experience. Would the site with better UX on mobile rank higher in mobile search?
As we mentioned in this particular change, you either have a mobile friendly page or not. It is based on the criteria we mentioned earlier, which are small font sizes, your tap targets/links to your buttons are too close together, readable content and your viewpoint. So if you have all of those and your site is mobile friendly then you benefit from the ranking change.
But as we mentioned earlier, there are over 200 different factors that determine ranking so we can’t just give you a yes or no answer with this. It depends on all the other attributes of your site, weather it is providing a great user experience or not. That is the same with desktop search, not isolated with mobile search.
They go on to explain that UX is important in general so get to it.
Forum discussion at Google+.