Lions mane has shown to cause neurogenesis and is not active. Psilocybin has a few other effects that seem to compliment the neurogenesis. Certainly needs to be studied more and I admit to feeding the hype a bit.
As far as why do we want to become smarter? That's a tough question as it seems to come with a cost. We have Amish communities where I live and though they lack in education, they certainly carry smiles on their bearded faces. It seems a lot of brilliant people are not the happiest and carry a heavy load on their shoulders. I think a happy life is a more valuable goal.