I suggest you take a much closer look at how power is consolidated in politics, and at how many of your elected officials greatly benefit from "career public service" for the duration of their lives (and their children's lives, in many cases). These points aside, you also appear to have a limited understanding of the fundamental desire for power over others; this is a characteristic that is frequently presented as a desire to "help" fellow citizens, when the end results are all too often anything but helpful.
I am certainly not opposed to people achieving great financial success, nor am I claiming that all or even most rich men desire elected office. It must still be noted that elected representatives, especially but certainly not limited to those holding certain federal offices, already heavily tend toward possession of far greater financial resources than the majority of the people they govern. The GGP suggestion that campaign contributions should be made illegal would only serve to further increase that trend, which is an outcome I believe NoKaOi would be unhappy with.
"Boss" Tweed serves as an interesting case study in some of these points. Unfortunately, while the sheer magnitude of his transgressions outstripped those of most of his contemporaries, his behavioral patterns remain disconcertingly common among politicians in the present day. This is an unfortunate side effect of basic human nature having remained wholly unchanged in the interim.