It would not work because the scenario you describe would amount to seeing "all your productivity evaporate into a never-ending haggle over tasks." Also you presume that you can be good at estimation and assigning "value," but everyone actually sucks at that. That's not to say that no one can accurately estimate anything, it means everyone sucks at estimating when it really matters. Your idea also kneecaps your ability to delegate, and motivates pay-later kinds of corner cutting.