Historically library usage has been surveilled, so I would say that making passive surveillance of your users more difficult is a 'valid reason' for going through the trouble.

You don't need logins/user accounts for your users to be identified. IP is sufficient in many cases, and browser fingerprint pretty much covers the other cases.

Also, if the website ever has need to become more complex, it will be easier and less error prone not to have to throw 'figure out how to implement TLS' on the pile of tasks.

Also, if permissions are the primary concern, might I recommend moving to a host that does SSL/TLS for you? Webhosts have come a long way in the last few years. Moving to a nicer one may actually save you effort in the long run.