From an SEO perspective, google is updating all teh time and reliance on linkbuilding is dangerous as we have just seen with a key client.
Google still recommend a link building stratgy but suggest you diversify into PR and social media to build page rank. That means you need to create great content and promote it.
From a conversion perspective, great contnet is not enough, it must also be relevant. Look through your email subject matter from your customers over the past year and match this with search queries in analytics (not keywords but actual terms they used to find you) and there's your relevant topic and inspiration. Now you gotta do it daily.
Don't forget contributing to other publishers (especially popular and high authority sites) also constitues as content. Curation is fine if relevant (check out scoop.it) but creation is always best, it takes time so allocate time!