I think it’s undisputable that the rest of us, at least, would be better off if there were 100 extra Bryan Caplans around. If nothing else, I’m sure he contributes more in tax revenue than he uses up in services.
The Darwinian question is interesting, and goes to Dawkins’s good Selfish Gene idea. Most of us don’t want a clone of ourselves– we want an almost-clone, but improved in certain ways. We would like our child to have higher IQ, no asthma, and no tendency to be pot-bellied. That would be bad, however, for our genes for stupidity, asthma, and pot-belliedness. There’s an inter-genetic conflict.
There’s also a good philosophic question. If my almost-clone is smart and non-asthmatic, is he really like me? Have I really perpetuated myself? What, especially, if I am centrally defined by my bad qualities—arrogance, cowardice, and stupidity?