Neal
Sharing links on social media is becoming more important to ranking as time progresses. So my view is the better you get at social now the more influence it will have on rankings now and down the track. EGOL has nailed its importance but I think social will only get more powerful on search/ranking influence.
Google is looking at ways to amplify social as it maybe the most pure (incorruptible) measurement tool for rankings. Earlier this year google & twitter announced they were re-connecting and google would have full access to the "firehose" or all tweets. Though yet we have not seen any significant changes in causation between ranking and tweets google will be working on something given the open funnel they now have into twitter.
Positive social shares validate a website and inform google your website is relevant, current and being talked about.
Moz published the slideshare below, which maybe helpful.
http://www.slideshare.net/jennifersablelopez/social-medias-influence-on-search-going-beyond-rankings
So I recommend think less about the technical side of nofollow links and more about the positive aspects of social media ie driving traffic to your website, creating links by sharing and then owning the space as the of power social to SEO is amped up.