A good point to make would be that we don't actually know if we gain this additional brain tissue, including all the extra synapses and activity, because of the intellectual behavior exhibited during life or whether it's because those born with those types of brains choose those behaviors. It might also be worth pointing out that we measure a person's intelligence based on the ability to experience life in a varying range of detailed complexity. The mentally challenged near the lower end and the genius abiding in at the top. Now whether this would have a bearing on how detailed or incredible an individual's psychedelic experience I believe is the wrong question. Each person experiences life in a degree of complexity only relative to itself.
As Huxley says, "We're all island universes" and each perspective is only worth aesthetic value. Basically each person wagers other's complexity only according to it's relation to it's own. So is this question even valid? I understand what's it asking to know, but I don't think we're asking it the right way. I think someone could quickly say, "Yes, the smarter you are, the more complex your brain, the more extraordinary your trips will be." but I think this is little more than saying, "The more you've got to work with the more you've got to work with." Just seems redundant or maybe just obvious. Fascinating topic.
With that said... I wonder what kind of trip Hawking would have! I bet it would rule.