JIRA does not have any view tracking functions - who is looking at it is mostly irrelevant for the purposes which JIRA is designed and used.
If you want view tracking, you need to enable that by logging the urls your users hit (most of us do that by changing the logging settings in the Apache/nginx/IIS sitting in front of JIRA - I suspect you can do it with the Tomcat too, but I've never really tried because I usually have it behind a web-server)
You can probably see that the answer to "unused boards" falls out of that - there's no way to find them, because you don't know who is visiting what you do have.
I usually change the names of "dead" users to indicate that they are no longer active, and then use the Admin options to identify and delete their dashboards...
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