Here's what I think:
-Having a small player base is actually what makes UN appealing. Yes it's a bad thing as a business, but as a server knowing and seeing familiar faces is a lot more fun than having random people.
-The events are the main attraction for me. They're hosted a lot and give a constant activity to do. They have a wide variety and are generally fun. These wouldn't be as inclusive and entertaining with more players.
-The items. They have a ton of cool items like emitters, portal guns, and other "mess with players" stuff like the ban hammer. These would get extremely annoying with a big player base. But as it is now, it's perfectly fine and cool to see.