A no-plugin server sounds like a good idea, but with any number of users, it quickly becomes not-so-much. You don't need much, but some kind of Permissions plugin, and some functions of Essentials seems a given to me. I'd like to hear how it turns out if you manage without them completely for any length of time, though.
I'm still running my small server, and we've still got a few spots for any mature players interested in joining us. Contact me for details. (But we use plugins. )