Yet, strangely, the people who want to sell me crap never let me cash in directly on my personal information. They always want to buy through some middleman that claims to be offering me some other service.

A Blippy analog that monetized and promised you 10% of the take would probably be insanely popular.

If I could put a dollar amount on my internet reputation that would be very valuable to me. I reckon that's something I could put to good use.

This does the reverse. It doesn't put a dollar amount on your internet reputation. It develops an internet reputation based on your dollar amounts.

Then they will monetize by giving it to the only people who really care how much you spend at Starbucks: Starbucks (and competitors).