Both Facebook and Twitter are already polluted with spammers and spambots. Doesn't matter - their effect can be filtered out because the natural follow-on signals from real social engagement cannot be easily faked, just as a balanced backlink profile cannot be faked.
There really is another mindset at work, and I'm struggling here to communicate it clearly. Because it is truly another online marketing paradigm and not traditional SEO, it's not easy to make the shift. It took me a while, that's for sure.
In another thread in the Twitter forum about their change of CEO, one reply asked "why does a website needs a CEO?" That's the old paradigm asking, not being able to think of a website as a business in the fullest sense.
A business needs partners, allies, friends. A website? Not so much, especially under the past paradigm - the one that Google has begun to dismantle. And how do you find partners, allies, and friends at the scale online marketing really needs? Social media, that's how.