Sales taxes are regressive to great degree. They force the poorer people to pay a greater percentage of their income in taxes than the affluent.
In general what you are proposing is a very Libertarian form of taxation. The major flaw in such a system is that it ignores the communal interest (the majority) by focusing more on the values of the individual. Such a system is workable, but brakes down very quickly when placed under an economic stress such a disaster, war, or large scale projects. It also relies on an assumption that we can precisely measure the value of each good/service which is practically impossible, even without marginal utility factors.
It is a utopian solution, but unworkable in practice.