Whether you have a B2C or B2B model, you should demand accountability from social media marketing just as you would other channels. Even if you're not investing in paid social activity, there's still an opportunity cost - right?
What we've learned works best, is not to think about social media efforts alone, but instead as part of integrated campaigns. Some social campaign efforts are simply intended to increase awareness, establish identity, thought leadership communities of interest, etc. That's OK. It's "top of funnel" activity that can thoughtfully guide prospects to other content in your campaign, such as an eBook, Slideshare or demo video.
As you track conversions from 'snackable' to more robust content, you'll gain greater insight into prospect's specific interests and become better able to target trial offers, etc. Many won't be ready when you want, but you can always re-direct them into 'nurture' campaigns until they're ready to advance in your sales cycle. Just make sure you have a flexible marketing automation solution, like Hubspot, Eloqua, etc. to manage the process more easily.