I really despise facebook and twitter. It's a personality thing I am sure. I find it also addictive and confusing. It feels like many of the agents and other writers and youtubers etc, they just are sort of using each other for numbers or something. Does that really work? Do numbers of followers equate to sales really? Many of the writers I followed seemed more like tweeters than real writers. I want to be joyful about my career path and it feels like facebook and twitter suck that away and un-motivate me. Could I just have my platform efforts be selective as I go along, just youtube and a blog? Vlogging is a lot of fun. I could do it regularly and improve at it. Is it necessary I try to gather numbers of followers and friends? I know you have said it doesn't matter in some ways, but I also think it seems to. There is so much referring to twitter and facebook.
It's ok to despise Facebook and Twitter. It's NOT ok to ignore them as useful tools. When your book
is published, you'll want to be skilled in a variety of social media platforms because you want to be able to reach your readers where THEY are, not where you are.
That said, it's totally ok to prefer one platform to another as you start out. Get good on one, learn another. If you're good at vlogging, and youtubing, build your audience there. Then learn how to promote your vlogging and youtbuing on Facebook and Twitter. You don't have to like it to utilize it.
As to whether it sells books: like all publicity methods there is no way to quantify results. I know that drives many people nuts. (Some of those people are my clients in fact.) My philosphy as a publicist (back in the day) was "do everything you can to promote your book, and then one more thing." Sometimes it works, sometimes it doesn't. I do know for an ironclad fact that people don't buy books they've never heard of.