I have an idea. Have a server host the mod The Crucible.
Also, change the server up even more than you did before. Try the weapon and vehicle replacement mutators and add new weapons and vehicles to UT3 maps, custom or otherwise.
Try not to rely too heavily on UT3 versions of UT2004 gametypes like JailBreak and Double Domination. If you
do choose to rely on this, mix weapons from other weapon packs to keep it new.
And just for kicks, maybe have a match where you play with overkill versions of the UT3 weapons.
I know it seems like I'm just talking about changing up the weapons, but there's a reason for that. You had a lot of different custom maps and gametypes, but as far as I know, you guys kept the weapons the same. Basically, I'm suggesting you try changing the weapons up a bit to keep the gameplay fresh.