I was wondering if I should set up a secure connection for the db administration application (phpmyadmin) for my sites.
They don't store credit cards nor anything that could be valuable for a hacker.
They're fairly rare, unless you access it over a wireless system. On the other hand, setting up a self-signed SSL certificate is pretty simple and raises the effort required to do a MITM attack, so there's no good reason not to do it.
Does it store passwords? Could compromising your (or some users') password compromise other sites? That's the main risk.