This experiment was wrong from the start; no record-keeping or attempts at training, not to mention giving him cannabis and alcohol, which was totally idiotic. It also looks like Terrace was completely unaware of chimpanzee's normal development and blithely disregarded any consequences of this. There have been better results, more notably from Koko (admittantly a gorilla rather than a chimpanzee) who had a devoted keeper and trainer. The experiment seems to work at some level, given that Nim was apparently teaching his fellow chimpanzees sign language. How tragic for them all that they were used as experimental animals.
Even though this animal likes marijuana, he is still just an animal. They are good test subjects because they are more like humans than any other species, so testing some things on them might be able to really help the suffering of humans. We can learn from watching a chimp ask for marijuana.
The fact that chimps are smart is the perfect reason to use them as test subjects. They tend to come somewhat close in many respects to human subjects and the data that is yielded from such testing is invaluable to human beings. I say we continue to use them as test subjects. Especially if they're smart enough to smoke pot.
Chimps are not to smart to be test subjects. I can not conceive of an instance in which any person or animal could be "too smart" to study. If done correctly, we can only advance our understandings as well as the lives of the subjects if we properly study them and give them every opportunity to teach us.