Using cookie to track users

Tracking a visitor has nothing to do with authentication...

For simple statistics the easiest thing you could do is use a session and store each pageview in a database with a timestamp, session_id and current url. That way you can track how many pages an average user visists etc.
But you could just rely on some external statistics like Google analytics, Piwik etc.

Using authentication is the most complete and proper way.
Because session is on, ip is recorded etc...

No SEO spam