If we are comparing a regular $40-$20 software sale to pay-by-tracking, then the people being tracked need to generate personal information that is worth equal amounts. It need to have mass market appeal in order to generate billions. How will pennies per day tool-bars do that?
Further, I believe a service like Google Contributor does what you're implying, but it doesn't get much press - which doesn't surprise me: the overall market deems free content worth that privacy "trade-off."
I don't understand why this is necessarily a "bad" thing -- it's like the equivalent of a real-estate broker telling me that 10/20 houses on a block have 2 bedrooms, and the other 10 have 3 bedrooms, even though I know nothing about the people living in those houses.
How many people will accept the deal, and why doesn't it already exist?
Or to ask a different question, will companies demand $20 for the services instead of offering it for tracking-as-payment? How will they fare against less polished services that are given away for free by people who run it on their spare time?