I think that _initially_ this new neural growth can be co-opted into general mental flexibility, particularly for things like mathematics and visual reasoning. In a sense, varied movement makes you more aware/perceptive of space. However, I think over time if you don't try to utilize your increased spatial awareness to solve spatial problems, eventually those new neurons will prune their synaptic connections to make the network as efficient as possible. Thus, I believe that pairing novel mental and physical training is the best bet for improving overall intellectual abilities.