Twitter used to help a new site get indexed by Google a little faster, I don't think that it makes much of a difference now.
Pinterest links can show up as follow links, and a lot businesses use them to showcase products and link directly back to a product page for conversion. That's better than SEO frankly. Closing the loop for a quicker transaction.
I agree that you should focus on using these channels for the value they provide on their own, not for trying to game a particular search. I do think that there is value in SEO for creating these profiles, branded search is still important and it's always good to create potential SERP results for you brand.
