Although I have an IG account, it was mainly set up as research for a novel (character becomes obsessed with a similar social media site to IG), but I've been using it to micro-blog the books I've been reading and I've grown rather fond of it as a record of what I've read over the last year or two.
But Book Twitter is quite something. I'm definitely influenced in my reading habits by the titles I see mentioned/promoted online. And what's rather lovely is that, for the most part, there's a great deal of kindness and mutual support among writerly tweeters. And it proliferates beyond writers: librarians, literature teachers, bloggers, reading enthusiasts, the publishing industry etc. all get on board, and there's a definite sense of community which I'm starting to find really helpful. I've discovered loads of useful tips, sites, supporters, books, new contacts etc. via Book Twitter.
Sometimes it's not so much the content, it's about how you participate in the conversation. If you've got pertinent or entertaining things to share, people will be happy to have you on their team and with the extra visibility comes extra opportunity. So it's worth persevering.
Sorry, bit of a swerve! I think the long and short of it is that you'll get more out of social media if you do it for the fun, not just for the promotional oppportunities. The tweeters that simply spurt out book adverts are the ones I tend to ignore because they're not very interesting. The ones that share a book cover full of genuine excitement/admiration/pride etc. will tend to grab me and make me seriously consider buying or downloading them.