as mentioned previously, a lot of nail polish removers are no longer acetone-based. Some just have strong alcohol content.....definitely gotta read the bottle or an Material Safety Data Sheet....I read one bottle that said it contained water
So granted, the acetone could "help" with MPG, I'm guessing the water would negate it....hehe, water in the tank isn't good at all.
As stated, if you do try it, better off going to the hardware aisle and buying the half gallon.
My concern would be proper storing and measurement for use at the pump. You'd need an acetone-safe (non-plastic basically....) syringe or measuring glass + funnel to do it safely and accurately.
The closest I go to nail polish/acetone was Berryman's B-12 CHEMTOOL, which contains Acetone, Methanol, Xylene, and some other chemicals. Seemed safer, since the product is marketed as a gas additive...
As far as acetone safely used in the fuel system, some say it can deteroriate plastics/rubber that it comes in contact with; but others say the 5 or so oz. of acetone, diluted over 10-20 gallons is unlikely to cause any harm. BUT, there was some "acetone test site" in which someone reported an issue with, I think, a Toyota Prius; supposidely they have a rubber/plastic "bladder" in the tank, and the acetone ate away the bladder over time....