Yeah, it seems clear to me that there have to be limits, and the concept of money as speech just does not work for me at all. I like to think that if all the major candidates had the same money to spend, then the quality of elections would go up. The obvious problem is figuring out how to limit things in a way SCOTUS would allow.
And that still doesn't solve many of the other problems with campaign finance.
For example, lets say you give every candidate a $50 million dollar limit to use for campaigning.
What's to then stop, say, Exxon from going out and putting out a commercial, not sponsored by a campaign, supporting a candidate? Or stop PETA? Or the NRA? Or a local group in your home town buying money to put an ad in the paper because they feel strong about a candidate?
See, that's the part that I see more about speech than the money. The ability to go out and say "I like this guy and I think you should vote for this guy for this reason" or "I don't like this guy, etc etc".
Just off the top of my head as far as a limits system....
There was over $800 million dollars spent last year just between McCain and Obama. Limit candidates to a total of $100 million. Additionally, put a small tax of maybe 2.5% on all political donations that goes into a specific fund that is untouchable save for some specific reasons.
Any party that recieved, lets say 5%, of the popular vote in the previous Presidential election and spent less than $25 million will recieve $5 million from that fund.
Once this gets underway for a bit, during the 2nd year of the current Presidentail cycle any of the money in the account in excess of what is needed would go straight to paying down the national debt.
The nice thing with this is you could almost garauntee that the two main party candidates will raise their full portion each time, which would result in an extra $5 million going into that pot.
So come the 2nd year of that Presidential cycle if there is no one that met the criteria (5% of the vote, less than 25 mil) then that money goes to paying down the debt. If there is, it stays there and goes to them the next election.
This would hopefully encourage people to vote third party if they agreed with that party, as now suddenly that vote DOES matter because you can try to get your 3rd party into range to get the bit of financing. It shouldn't have a big effect on "small" donations because if you donate $10 to your local politician cause its all you can afford your politician would still get $9.75 of it and the pot would get a quarter, hardly squelching even the voice of the poorest of poor.
If it started looking like more than one third party would become viable like this you could raise the tax on the campaigns to 5%, thus accounting potentially for 2 "third" parties. I would max it out at that, and add in some kidn of adendum so that it goes in descending order from the highest, but qualified party, to the lowest, until there's no further money left.
Just an idea shot from the hip there to try and limit at least the spending of the campaign itself, make third party votes worth while, and possibly get third parties somewhat further injected into the whole ordeal. That said, it'd still have a ton of holes.