Personally I think that a simple, Minimizable GUI that shows all the information for each player. Allows you to Kick, Ban players, Change General Server information and other admin commands.
GUI's just make it easier when doing things server side, by all means if you want to use commands that function should also be available
Or
A Web Interface on a chosen port so when the ip is put into a web-browser and the port an administrator can login and edit the game settings there and maybe a Live map with info about all the players.
All it needs to be is something like this (The Live for Speed Server GUI)
Several tabs that have editable settings
A GUI would have very little effect on me because I have a 32GB Ram 8 Core Server :)