Not only does acetone not increase your gas mileage, it actually DECREASES gas mileage.
I kept track of the gas mileage for each tank for the past several tanks. Here were the results...
Guess which one is the acetone tank? You guessed it. The tank where I got 16.9 mpg. The 17.9 tank was mostly interstate driving, including one part where I thought I was in 5th gear when I was actually in 4th, and set the cruise and drove for about 15 miles with the engine revving over 3000 rpm. In the Jeep, of course, you don't hear engine noise at 70 mph; you only hear the violent rustling of the ragtop.
So, there you have it. Unless there's something I missed or did incorrectly, acetone will only hurt the gas mileage in the Jeep.
Is this scientifically conclusive? Probably not, but with gas at it's current price, I can't afford to find out.