One way to give raids more variation is to give the raiders different motivations. Some good ideas have already been posted in this thread! Each different kind of enemy should create a different story for the player. These motivations could range from Slave Traders capturing colonists alive, to Bandits stealing resources, to Raiders trying to wipe out the colony. The idea of Smugglers setting up camp that Adamemnon suggested seems interesting as well. Also AspenShadow mentioned Assassins - having an enemy that specifically targeted one colonist is another interesting angle, particularly from a story perspective if it could be tied into that colonist's backstory.
Rather than having different enemies, I'd suggest using a table weighted by the "leader" background. First, each attacking group would have one designated leader - taking that one out would make it easier make the others turn tail. But more importantly, the character background would indicate the likely raid type: (going off memory of LP vids for types)
Medieval Lord - capture slaves
Medieval Oaf/anything else - general mayhem, steal anything of value, with alcohol, weapons & cash a priority.
Urbworld - take anything of value, may or may not take slaves
Assassin - target a specific Colonist, and kill anyone in the way
Of course, it might be easier to just have different preset enemies, so that might be a horrible idea to implement.
