There's one Medal of Honor: Allied Assault SpearHead server in particular that I've been playing on for 12 years.
It's dead all day, but at night, the server owner and 3-4 regulars are ALWAYS there, 5-7 days a week. Then 6 or 7 more people will come and go throughout the night, with a solid population of 7-10 people on for a few hours - all for a game that is almost 17 years old and down to a few hundred left that play even monthly.
I think that's a big part of that building a "community," the server doesn't have to be populated all the time, but if it's populated consistently at a critical time - like, for example, 8 to 11 p.m. 6 days a week - you'll find you'll build a reliable group of people who enjoy the server and, over time, will start to log on during that window and "expect" it to be populated, and even when it isn't, they will sit there as a 1/16 and wait for the "regulars" to join, because they know it's a consistently fun server and it's worth spending 10-20 minutes sitting there by yourself to build it up.
When you've reached that point, you're a success - doesn't have to be 21/21 all the time; a regular group of 5-10 people who play often together at a consistent time is a pretty awesome server that will attracted others to it.
The other element, aside from the consistency/personal time to put in to ensure your server is populated regularly, is exactly what you asked about here: having attractive settings. As much as I've come to dislike Arsenal, having it and LTK, etc. in the rotation every few maps isn't necessarily an awful thing, as when it does come time for Arsenal and LTK to come up, you'll probably keep your loyal crowd, AND you'll pick up a couple of the Arsenal regulars who might stay for a while and enjoy the change of pace!