It sounds like a cool idea but it would depend on what you do with the car that you corner balance on that scale.
assuming a car ways 2500lbs and 60% of that weight is on the rear tires (911) and the scales are off by 5% then each rear scale could be off by about 40lbs and the fronts about 25lbs. This is of course making a lot of assumptions like the weight being evenly distributed between the two rear tires etc. For a street car I think that is accurate enough. I personally prefer more accuracy for a track car. Keep in mind that my math may be off and the rest of it is my personal opinion
Still a really cool alternative to paying gobs of money on a set of scales especially if you could make them more accurate than 5% Maybe you could build one and test how accurate it is before you build the other three.