EDIT: STV would also take power from political parties in multi-party systems, since people can vote for different candidates in different parties, and list the preferred party as the last choice.
The highly gerrymandered districts in most states (70% are safe for one party or the other) seem to be a bigger problem to me.
The only constitutional amendment I would love at this point would be something along the lines of all districts must start at the northwest corner and be as close to boxes as community and terrain allow.
Basically, I can see your scenario of a noble candidate who can only get funded by one noble wealthy patron, but I think that will basically never happen compared to outright bribery which will happen all the time.
I'm inherently suspicious of any politician that's funded by only a few people. You know they have the candidate/congressman on speed dial, and the candidate/congressman knows how important they are. It's a built in conflict of interest. Numerous small-dollar donations, on the other hand, tend to reflect actual democratic interest in a candidate -- even if it's a machine, at least they put in the work to build the machine, lots of retail politics helping lots of little people.
Right now the corporations, unions, and political parties have ways of spending large sums of money, but the individual doesn't. I don't see how allowing individuals changes the possibility of influence peddling. Do you not believe that a Congressman is currently capable of refusing to take a call from an important union boss?
"Numerous small-dollar donations, on the other hand, tend to reflect actual democratic interest in a candidate" - maybe. Funding wise the Republicans go more that way than the Democrats (strange, but disclosures sometimes tell a weird story).
Unions and political parties are collections of individuals who've organized for an expressly political purpose. Corporations aren't, and for everything they've accomplished, they have terrible incentives as regards the political sphere. The ROI is huge if, for a measly few million, you can swing a vote of congress.
RE: Republicans and Democrats, my information was that Democrats had done better in the small-donor game since 2006, but I could be wrong. Regardless, my opinion is out of small-d democratic principles, I'd feel the same way about it if it hurt the democrats -- that would just mean we had to do a better job of appealing to ordinary people and spend less time appealing to the big money people.
No, unions are bargaining groups for workers. They have as much / little right to politics as corporations. Corporations are groups of shareholders and the days of normal people not owning stock are long over. Look at the hold of certain unions in California and their pension system woes for an example of undue influence that is going to bite someone.
"Never doubt that a small group of thoughtful, committed people can change the world. Indeed, it is the only thing that ever has." -- Margaret Mead
People need to be able to start revolutions without the use of arms, and for US politics that means spending money. I find the preference for parties and unions to be a poor substitute for individual rights.