I have been on LinkedIn for a couple decades - mostly on the free account. If your getting more than 1 email a day from anyone other than your direct connections you have something set wrong.
I only get 1 update from linkedin a day - with people wanting to connect - mostly spammers which I can click ignore. I do get email notifications from people I know / knew - and I have to click on linkedin to read their message.
The paid service is if you want to connect with people outside your current network. I got a free trial of the service years ago - I was able to find some people I knew in college and connect with them - they were not in my professional network.
That said, the paid service I think is for recruiters or someone trying to network into a new industry or find the correct person to network with. I know some programmers that get all their work from Linkedin. They like to do piece work - no job more than 30 days for example. I however only link in with I have met in person.
Its a great place to keep track of people you worked with in the past. I have literally worked with hundreds of people on one time projects years ago that I can still be in touch with. People from college 25 years ago, etc. I have almost 1000 connections. These are all people i have worked with in a 25 year career that now live all over the world. There is no other place to keep track of these people and I would loose complete touch if not for linked.
I recently got an email from a girl I worked with 20 years ago. We were linked but likely hadn't spoken in proabably that long. She was looking for a job and asking about the area I lived now - she is completely out of my industry at this point. I was happy to answer her questions.
Its the only social media I go on - well besides automotive sites anonymously. I have no faceplant account, no instagram. I have a twitter account only to follow a couple financial channels - I never post.
It is what you make of it and its not for everyone.