re: Congress shall make no law...
I'd say it's too late to close the barn door as you'd like. The separation of church and state was in the Consitution from the beginning; adding a similar amendment now regarding business would be impossible in the face of opposition from entrenched interests.
Besides, the analogy's imperfect, at least from my point of view. I know you'd like a prohibition about involvement in the economy that's as absolute as the one against religion, but you can tell from my arguments on this thread that I think completely unregulated capitalism would be a monstrous disaster. I'd fight such an amendment myself tooth-and-nail, for my reasons instead of entrenched interest.
You can't purchase favors from a government incapable of delivering them.
I think you missed my point about cause-and-effect. That power to deliver favors, which was missing in the beginning (except in the sense that there was no prohibition against it), grew over time because so many interests wanted it. And let's not forget that other interests than big business have pushed for other kinds of government intervention, in the form of consumer-interest regulation of business. Those two opposing interests both push in the direction of intervention. Sorry Tom, but you're tilting at windmills.