You need to bring in new faces to make things exciting. Start another faction apart from the player made one, recruit members, and start internal conflict.
You're ideas about protected shop areas and whatnot is great. It sounds like a well put together server. Most people are NOT looking for new mods and plug ins, they are looking for fun and excitement.
So all you have to do is find ways to keep conflict going and you'll find that your server will pick back up again.
I hope this helps! Cheers!
