Putting aside the dystopian angle for a minute, if you knew your data is valuable, would it change your behavior? e.g. if you behaved exactly the same as the median, would your data be valuable to advertisers? They gain no new info from you. Would you behave erratically just to make your data more valuable?

This kind of makes the theft of personal data even more insidious, IMO. Your data is only valuable if you forgot you’re being watched.