I think your analysis is half right: it explains why the rich are doing better, but not why the poor are doing worse. The latter is occurring because the shift of manufacturing to lower-cost countries has increasingly eliminated the possibility of middle class jobs for those without a college degree. Manufacturing jobs have been replaced with low-value-add service jobs, which naturally result in lower pay.

Even if we were to ratchet taxes on the wealthy back up, this wouldn't do anything to bring high-value-add manufacturing jobs back.