FOMO stands for Fear-of-missing-out. It works really well. If you want your product launches/e-commerce product campiagns to be effective then you need it. It works well when you combine it with product bundles and create a time-limited discount on it with some product testimonials.
Yes, you're right. But it's worth it on the long-run. Well, have you heard of Upviral? you can actually get a whole lot of email sign ups with upviral through referral campaigns.
Exactly. Level of engagement matters a whole lot. There are lots of fakes followers. Even most celebrity Influencers aren't so connected to their audience. There are analytics tool to determine quality Influencers though.