In evaluating Edward Conard's claims for the pro-social consequence of wealth-accumulation, maybe it helps to step back a little from the American scene.
If a Russian oligarch claimed that he had gained his riches in a way that enhanced the well-being of all Russians, most listeners would (I think) be skeptical. The richest Russians have gained their fortunes by appropriating former state property—and they hold their fortunes by corruption and violence.
If a very wealthy Chinese businessman made an equivalent claim, listeners would likely be more open to the possibility that it was true. Many of the richest Chinese do useful things: they manufacture devices, build improved housing, provide more comfortable and convenient shopping, etc. Even in the best cases, however, an inquiry would probably discover that large elements of corruption and exploitation played a part in the building of the business.
The point here is that the assessment of the morality of wealth depends at least as much upon the character of the surrounding society as upon the character of the wealth-possessor.
In the right institutional setting, the human propensity to "truck, barter, and exchange" can enhance the welfare of all. In other settings, it leads to plunder and pillage.
Conard's arguments about wealth, then, are also arguments about the character of American society over the past 20 years. If we discover that great fortunes have been made in antisocial ways—cough, Franklin Raines, cough—that leads us away from Conard's assertions to another question: What kind of institutions are needed to direct accumulation in directions that do enhance the well-being of the whole society—and how do we test that our institutions are indeed doing so?