You say:

Liberal political thought, to this point, has largely ignored a set of concerns that were central to most Labor movements, which might be called concerns over “workplace democracy” or what is sometimes called “democratic corporatism.” With some notable exceptions (Pateman, Gould, Mansbridge), frequently offered by those operating in a Marxist framework, political philosophers have instead focused on issues of distribution or issues of legitimacy in terms of public reasons or political dialogue. Relatively little attention has been paid to whether a society with profound inequalities in wealth, where corporations are dominant players in the political landscape, can be meaningfully democratic.

Sorry to quibble, but I don’t think this is true. Mill, to give one prominent example, was a strong proponent of worker cooperatives. In fact, many radical classical liberals of the nineteenth century were skeptical of the wage system (Lysander Spooner, Benjamin Tucker are some American cases) and worker cooperatives were widely discussed.

The worker cooperative idea largely arose from worries about the effects of the wage system, however, not from concerns about corporate domination of campaigns.

Also, Tom Christiano has a nice article on this matter in the current issue of Social Philosophy and Policy: The Uneasy Relationship Between Democracy and Capital.

As for the broader issue, what would be the reason for worrying about workers being left out of the loop when deciding whether corporate money should go to causes they don’t support? If the idea that because they contributed wealth to the firm that they thereby acquire an entitlement to a portion of decision-making within the firm?

I’d be interested to see such a principle worked out because the formulations I’m imagining seem to have odd consequences. For instance, if the idea is that when X contributes utility to productive venture Y that X thereby acquires a share in the utility produced by productive venture Y, one might wonder how a wage system of any kind could be justified.

Also, if workers add to the income of bosses while being paid a wage for their services, do they thereby acquire a right to dictate how the boss spends his income? Or is the idea that they somehow acquire title in the means of producing the wealth and so they thereby should have a say in decision-making? It’s hard to see how such a claim would go.

One more thing:

It is no longer plausible (if it ever was) in the American context, to believe that campaign finance law will insulate the political sphere from the economic sphere.

Is this really a good idea? Isn’t the idea to insulate the political sphere from unequal influence from the economic sphere? Of course economic interests should affect politics, but perhaps we’d want equality of impact (though Dworkin raises some concerns about equality of impact in Sovereign Virtue).