No follow backlinks do not help in increase SERP. But these links help only in increase a traffic on you page.
Google likes to see natural looking links, and having all Do Follow links no longer look natural in Google's eyes. Having a balance of Dofollow and Nofollow links does. There is an indirect positive effect on your SERP when you have Nofollow links
It's debatable, some people believe it may help, others firmly stand by the point that it does not help. In my view (not expert) regardless of do/nofollow links it will help overall as it's also about getting your brand out there.
Nofollow Links Are Not A Helping Source In Increasing SERP, But Help In Increasing Traffic For The Website.
You should maintain no-follow and do-follow links both, only do-follow links don't look natural in Search Engine eyes. However google also count no-follow links, if you check google webmaster tools you can see some no-follow sites in your backlinks list
Here is complete discussion about nofollow Backlinks., http://forums.digitalpoint.com/showthread.php?t=2367652
NoFollow link helps to look natural link building. If you only have DoFollow links, Google may penalize for unnatural link-building practice. Therefore you must have some numbers, i.e 15% back-links with No-follow links for guaranteed SEO.
The best and the most effective methods for best link building are: Social bookmarking, Forum posting, Blog commenting, Article submission and Link wheel.
Some people think no follow backlinks have no bearing on a site's rank but I think they do. A backlink is a backlink, whether do follow or no follow. It would still help your site get a backlink as well as traffic. My two cents. Have a good day!
As we need natural links so yes we need both nofollow and dofollow links for building natural links to our website.
I agree with affiliorama. If your site has a do follow only backlinkprofile its not natural. Every backlink from a decent quality, wether its nofollow or dofollow optimizes the overall authority of your website