Is it possible to buy AdWords traffic to your AdSense revenue driven site and make a positive ROI? Good question, ehhh? I assume it is possible but right now, I personally do not know anyone making a nice living on that.
A thread at Search Engine Watch Forums named adwords to adsense site - what is it worth discusses just that. Bhartzer says that he knows of plenty people "who have bought traffic via Adwords and tried to turn that traffic into revenue via Adsense. From what they tell me it doesn't work."
The contextual queen, JenStar explains why.
It would be hard to value it because click abritrage is so subject to market conditions - price you can buy traffic at, competition, what the AdSense ad targeting is like, is it affected heavily by smart pricing, etc.
Forum discussion at Search Engine Watch Forums.