The problem with "vote against incumbents", particularly in the era of Citizens United, is that you'll have just greased the revolving door and destroyed any incentive to not sell off everything that isn't nailed down.
The corporate sponsors of our government, the true problems in our system, would love to be able to stand up a new placeholder every cycle, to decry the excesses of the last, run on reform and have absolutely no illusions about gathering power for themselves, or see no benefit in doing right by the people casting the votes.
Reverse that SC decision, you harm speech like Michael Moore's.
To your other point, there would be no corporate sponsors if we didn't concentrate the government's power in Washington by forgetting we can solve local problems using local government, and if Washington actually let businesses compete fairly and not creating artificial barriers to entry, such as license fees, over-burdensome regulation, frivolous patents and high taxes.
The problem isn't just corporations, which BTW, except for monopolies, are a net benefit to society (otherwise they just disappear). The problem is that we vote for corrupt politicians who corrupt our laws and interfere with the market killing off bad corporations.
James Madison said "If men were angels, no government would be necessary." The corollary is that government is not comprised of angels, therefore we can't expect it to be necessarily better than corporations.
It's a tough line to walk, no question, but I think there are few "normal" people who don't think we have jumped the shark here.
I do agree that not voting in corrupt people (and really punishing those who are shown to be corrupt; not just reading a letter in Congress). More importantly, move the power and influence closer to the people. I have far more sway over my mayor than I do over the President, and I'd trust him with more of my money.
I just finished reading Peter Thiel's notes from his Startup class and he suggests almost all businesses are in fact monopolies, yet pretend not to be by competing in other environments. Google has a monopoly on search, FB a monopoly on social networking, etc. I don't know if I agree that either of them are complete monopolies, but the moat is certainly thick. In a perfect business world, shouldn't those be broken up if they are in fact monopolies?
There's nothing wrong with being a monopoly in the sense that you simply won by having the best product. Where monopolies needs tempering is when they use their power in one market to displace competitors in another market - such as Google accused of doing by giving prominence to search results from their own properties over competing ones.