You and I might, a prior, believe that they would be much more valuable, but after 10 years and with some of the sharpest minds in the world working on the problem, facebook has never once shown me an ad for something I wanted. I have as far as a recall only twice clicked on ad on google with intent to acquire the item (as opposed to just clicking on the ad rather than go to the homepage of a company).

If you could actually create ads for things that I would want, personalized ads are probably worth more. I just don't think it is possible with current technology.