It would be neat if a colonist with an addiction would have his chance to join adjusted based on the colonies stockpile of their drug of choice.
"Hi there moster raider, I see you like yourself some flake. We just happen to have oddles and oodles of the stuff, join us!"
Or "Yeah mister colonist, I'd love to join you guys, but I just gots to have my medicine and you guys aint got none!"