I have never used any CPC campaign and am quite happy with my rankings and my sales from my sites.
Good
SEO, good content and ethical practices brought me this far so I think I would just keep doing what I am doing.
Besides, there are countries where people cannot afford $ 100-00 a day on an ad campaign - our money is 6 times your money so it is just a matter of affordability. In South Africa my clients can't afford that type of money either.
Having said that, I have agreements with them that states that when we make money from the sites, we plough it back into advertising but CPC raise too many questions and we cannot afford to loose that type of money.
So I would rather buy links in the right places than use CPC until they found a way of tracking and controlling fraud.