With drugs like Ritalin there is a sweetspot. Some people (in the extreme case ADHD sufferers) have low levels of dopamine, and the drug can help them concentrate. Others already have high levels, and taking more hurts their study performance.

Under gwern's "temperature" theory, it seems the same should be true for this kind of LSD microdosing -- surely we should expect to see both people who benefit from additional creativity and people who already are creative enough?