I'm pretty sure the Ayres-Bulow plan would trigger a big increase in expenditures on lobbying. Here's why: If a bill threatens to cost, say, the tobacco industry $100 billion, the tobacco industry will spend up to $100 billion to defeat that bill. And if they can't spend it on supporting sympathetic candidates, they'll spend it another way. So as campaign contributions go down, lobbying expenditures go up. Is one form of influence-buying more destructive than the other? I dunno.
What's lacking here is what economists call a model—a logically tight story about a fictional world that is simple enough to understand in every detail but still complicated enough to mirror important truths about the world we actually live in. Given a model, we could trace out all the effects of the Ayres-Bulow plan in the fictional world and use those lessons as a starting point for an enlightened discussion. I tried writing down a good model for this problem, but it turned out to be really hard. I think it would make a great project for a Ph.D thesis. But until someone actually does the hard work of thinking this thing through, I have no idea what to make of it.