It depends on the ROI.
If you pay someone a salary, and their social media efforts are directly responsible for sales which give you a good return after factoring in the cost, then it's worthwhile.
You should be able to tell if this would be the case by looking at your existing social marketing efforts. If you're gaining sales from these platforms which come in at a reasonable cost/time per conversion, then scaling that up may work. However, if your social media efforts aren't bringing any sales in, then don't expect more of the same to change much.
As for social media's role in SEO, Matt Cutts has actually made a video stating that social media metrics are not a factor:
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However, previous to that in 2010, he said they were a factor.
Personally, I think social media metrics are a factor, but not in any sort of simple way. It's not about how many followers you have or how many tweets you send out. Google will crawl these social media platforms, take what they can in terms of authority and relevancy, and then factor these in with various weights. The amount of followers, likes, tweets and all of the rest are just too easy to manipulate to be taken at face value.
Mind you, I also believe that Google do factor in no-follow links as well. After all, they rely on the natural progress of the web to find signals which indicate the popularity and credibility of pages, and no-following links is a direct manipulation of that which makes their job a lot more difficult. I don't think they pass on link juice like any normal do-follow link, but I don't think they ignore them either.