1) Some anthropologists see intoxication as the natural state of man since fermentation was invented until just recently.(No, I don't have a link, although there was a Scientific American article about this within the last few years)
2) I have family (an uncle) who are active in AA. They tell me that this is well known in the AA community. Instead of a lot of bums and ex-cons (which there are), the most interesting observation is the number of doctors, lawyers, professors, etc -- professions that usually require a high degree of intelligence.
3) Freud was of the opinion that depressed/addicted people simply were better at understanding how crappy life was than other people. Of course, Freud was a coke-head, so take that with a grain of salt.
4) I've been toying with the idea that the junkie mentality produces more creative and intelligent works than the sober one. Take, for instance, all of the famous authors who are addicted. Or comedians. It seems like there is some hunger, some desperate reaching out that comes with addiction that translates well into creative efforts. It might sound bad, but I don't think Stevie King is as good now as when he used to be a junkie. Sames goes for Robin Williams. It's just a working hypothesis. I wouldn't use any of these observations to justify addictive behavior.