From my limited knowledge of chemistry and fuel substances, I would say that mixing acetone with gasoline makes it burn faster, not always conducive to higher mileage, except if something is hurting the ignition process to begin with. I'd also suspect that acetone, being a HIGHLY potent solvent would cause a myriad of problems with fuel line hoses and plastic parts... I generally shy away from using acetone to clean anything except for metal parts because it usually dissolves anything plastic... With the high cost of fuel system components, I would suspect that experimentation could become costly.
There have been myths about magic chemicals and other agents (like magnets around the fuel lines) that could dramatically increase fuel mileage for decades. One of the older ones says to stick moth balls into the fuel tank...
For the most part, those legends are just that -- legends. If there were some magic bullet that would instantly increase fuel mileage, the big companies would be all over it -- and it would come mandatory on the cars... Believe it or not, the manufactures are scrambling to meet federal fuel mileage guidelines and they would pick on on anything INSTANTLY that would gain them the desired results... You'd see the stuff on NASCAR rides, and at the drag strip (nitromethane is a prime example -- but that stuff is so highly explosive that you can't run it at home -- and it is also corrosive -- but they don't care -- they tear down the engines after every pass!).
Mostly, economy is a ratio between the weight and wind resistance of the car, versus the cubic inches, volumetric efficiency of the engine, and rpm levels that it turns. It is mostly physics, with a certain number of BTU's of energy produced at a certain level of compression, when lit by a sufficient spark at the proper time, minus the rotating frictional losses of the engine and other frictional losses of the car. Get as much of that right as you can and your mileage will increase, hence the advice of some here on the board to run true synthetic oils, add proper air management devices to the vehicle, and tune it for optimum efficiency, plus air tires properly, run a size conducive to mileage instead of looks, and use a good grade of gas, sufficient in octane (but not over = costs more $$) what is needed by the engine.
