For what purpose? If you use it to help with connecting to people and staying in touch, yes. It doesn't replace the main ways you connect though: conferences and other meetings where you connect face to face, and connecting through shared efforts on Open Source projects, standards, etc.
Yes, there are recruiter spammers. Ignore them, or better yet fire off a polite "Not interested right now, but who knows down the line." type of email. It never hurts to keep doors open.
For advertising your project on LinkedIn, no..that's not where I see value in LinkedIn for most people.
Advertise your project instead in the relevant forums for your language, toolkit, interest. For example, make something that developers or startups might find interesting? Post it on HN with a Show HN. Make some new Rust crate? Post it on /r/rust, or Rust Weekly. Launch a new MVP site? Post it on Techcrunch and HN.
Individual communities such as telecom, ICS, geospatial, defense, etc. have their own forums to post on.
The more utility what you create has for others, and the more freedom you give others to leverage that utility, the more your project will get your name out there.
Another way of thinking about it: don't worry about optimizing your brand right now, create useful interesting things, let the people who share your interest in those types of things know about them, and incorporate any feedback you receive into new things. Also, make yourself available to help people learning the things you've already learned.
