Adding acetone to your gas, in a laboratory or other controlled situation, has never been shown to yield improved mileage.
Real-world improvements to fuel economy are typically attributed to placebo effects or inaccurate measurements. Additionally, acetone is a very corrosive material and can damage any rubber parts in your fuel system over the long run (gaskets, etc.), not to mention the damage it can do if you happen to get any on your paint.
If adding acetone increases your mileage, go for it. Just know it isn't anything the acetone is doing for you