Actually I agree with all of this - there's a tremendous difference between average intelligence and the top end of the bell curve, and we have no reason not to think it can't go higher. We are the first species on this planet to attain general purpose intelligence, and there's no good reason at all to think that either more isn't possible, or indeed that the process of human evolution in this respect has stopped - quite the reverse I suspect. We have every reason to assume that at the moment human intelligence is evolving like mad - it's being very strongly selected for in a very large gene pool.

But my point is that this all has nothing to do with the proposed methods of improving the brain. If we really knew how it worked, and were able to model the consequences of our actions better, then it would be less of a guessing game whether there was a longer term price to the short term gain.