not to mention the fan would only be usefull if the machine wasn't moving or moving fast enough to get air through the radiator.. (who rides a banshee slow anyway?)
Lighting upgrades isn't a bad idea if you ride at night and what not but I dont think I'd look into adding a fan. Like snop said, Get a after market radiator and a billet impellar and you'll be more then set in the cooling department.