Cognitive enhancement could come in two forms; it could help us think faster or improve our memory. We would have more of what we already have. It could also allow our minds to work in entirely new ways that we could never imagine with our current puny brains.
Both seem likely to me. We are all evolved from the same little clay crystal or electrified methane molecule (or whatever) that had less capacity for empathy or abstract thought than most of us today and we aren't so great that we couldn't be further improved.
One of the possible arguments against cognitive enhancement is that it would probably be expensive and thus out of reach to the poor; this would increase inequality. People who dislike discussing IQ and the fact that it is correlated with income will surely not like cognitive enhancement.
I don't want to downplay the challenges raised by a cognitively enhanced elite, but here are some thoughts. Most innovations were initially available to the rich. TV's cost more than cars when they first appeared and however crap you think today's TV is, it was worse then. But now most poor people have access to TV and it isn't seen as bad for inequality. The same is true for plenty other innovations, especially medical advances. Money incentive helps these things being invented in the first places which is surely good.
I often hear complaints that people lack the imagination or empathy to fully realise the plight of the very poor. I would guess that the same people would be suspicious of cognitive enhancement. Our increased capacity should help us better understand the plight of the poor and be better equipped to do sensible things about it.
Or would we only enhance the money making parts of our mind?