Usability guru Jakob Nielson is not in favor of writing content for search traffic:

If you’re an expert who wants to live from adding to the world’s knowledge, you must go beyond the mainstream Web model of single page visits driven by search traffic. You must change the game and create content that’s so valuable that business users are willing to pay for it.

You should also focus on material that lower-ranked content contributors can’t easily create in their spare time.

Both of these needs are met when you produce in-depth content. Link