I do believe it is possible to create strategic advantage by delivering great content and executing a social media initiative well. But the entry barriers to creating a Facebook page and initiating engagement, for example, are so low, I think it is unlikely that this can truly be "strategic." Engagement should more likely be viewed as a tactic that supports an over-arching marketing strategy, unless you truly have some super-human community management skills that consistently bring customers in the door.
Social media's place in the marketing mix is to provide consistent, small provocations and conversations through content that lead to engagement and interactions. Skillfully done, that engagement ultimately results in consumer interest, and hopefully loyalty and meaningful activity (like a purchase).
Take marketing out and replace it with journalism or content strategy - and it still works.