Well, agreed for the common Joe, but that still allows someone with a net worth in the tens of Billions to throw money around. Especially because these people have a clear conflict of interest.

They should ban money contributions completely. Each party gets the same budget (say 10M$ and you run your campaign until you have money and that's it).

You as a citizen wants to donate? Go and collect signatures, spread the word or stuff like that, but no money (IMHO).