Content is very important for SEO and retaining visitors.
For SEO: If your content is good then Search Engines will give your keywords a higher rank.
For Visitors: If your content quality is good, then your visitors will definitely return for more.
Personally, when I see a site in search results that use to have quality content then I will prefer visiting it for what I'm searching for.
I believe quality content is backbone to any web site. If a site start loosing quality of what it delivers, then it means the site is going to loose both visitors and rank in Search Engine.