I personally get zero value out of LinkedIn except as a place to control the info about my resume that people see. I don't want a "better" replacement because those exist already and just lack the user base.
With all the life coaches, "content marketing" and "SEO" specialists, "business development" people, I find the barrier to staying on LinkedIn is really bad.
When it comes to B2B marketing I spent a lot of time on LinkedIn which was a big waste; I switched to another channel and things turned around immediately.
Similar to FB - it's good to stay connected to old friends, former colleagues, random nice people you meet at conferences. Useful should you need to ping these individuals for info.