I see where you’re going here, but I think maybe there’s another way of systemically addressing the issue — less government.
That is to say, if it was not so lucrative for large companies to lobby for anti-competitive rules, or special interest groups to lobby for various wealth transfers, through the legislative process and government intervention, they simply wouldn’t do it. By having a government that can pick winners and losers, it makes any profit oriented endeavor more interested in leveraging it.
I go back to Bastiat (forgive him for being French), who noted that the proper place of government, that is the collective use of force in defense of private property rights, would create a system that did not encourage legal plunder.
So before we fiddle with where the money comes from in large campaigns, maybe we can instead look at reducing the incentive for that kind of influence purchasing? If government couldn’t force you to buy something, or force you not to buy something, or transfer wealth from on person’s pockets into another’s, we wouldn’t have a system worth spending large amounts money on.
Heck, if anything, the fact that the big money in 2016 failed to win the Presidential election is something that should give us all a bit of relief :)