What if we require that every $1 spent by someone on a political ad must also be balanced by a $1 subsidy for the opponents' ads? Seems fair to me and would reduce the impact of money. (I'm sorry but I forgot who proposed this idea.)
I'm not trying to be mean, just pointing out an unintended consequence of such a system.
(This would do nothing about money buying influence — as long as the donors are known, their wishes would be carried out by at least the major parties)