> The jump is from "wealth inequality" to "power inequality." It's not clear that the former causes the latter.

Well, there is that paper from Gilens and Page that argues otherwise (http://www.princeton.edu/~mgilens/Gilens%20homepage%20materi...):

    Multivariate analysis indicates that economic elites and organized
    groups representing business interests have substantial independent
    impacts on U.S. government policy, while average citizens and 
    mass-based interest groups have little or no independent influence.