No, the right of a person, a collective to give money is the same as their right to put up a poster for them or speak in their favor, or change their name to "Ron Paul", in other words it is a form of self-expression.
I think goes right to the point. How could one restrict an individual spending what they want to make a political statement? It's the core of why free speech is in the First Amendment - it's to ensure freedom of political speech.
I think the best remedy is to limit time. There's only so much one can do to get a message across in a limited time, even with unlimited money. Force a later start to the formal process with a compressed primary and general campaign.