Maybe letting people know how stupidly easy it is to modify ingame textures would help as well as letting them know that they can share said textures to the world by uploading them to this website (whenever that section actually gets finished)
let's face it, everyone loves showing off what they have made
I mean that's one of the reasons I really got into TSR and APB (besides how F++king AWESOME W3D games generally are)
Getting onto Steam would probably help too, especially if you got Steam workshop support working (EVERYONE loves Steam workshop)
Throw in map making, with a chance to have your map included in the official lineup, Devs who listen to the community and sometimes implement ideas if they are really good as well as feasible and show off/stage some epic battles for trailers and huzzah, more players arrive for the meat grinder fun.
Also mention it's free and a very small download size.