Content is important for obtaining large reader ships and returning visitors. But over the years I’ve seen many sites that have page after page of 100% unique content but still fail to get over 200 uniques a day. In saying this, I’ve also seen small niche sites with correct SEO done that can pull 300-500 uniques from search engines from multiple keywords.
So SEO does play a major role in any site. But no serious Webmaster in the years to come can just rely on their content.