In general people who are trying to prove a mileage increase also tend
to drive more conservatively which may improve mileage more than additives.
I think if you figure in the cost of the acetone, the risk of it taking
paint off your car and deposits out of your tank and into more sensitive
areas of your fuel system, and its bad effect on hoses, seals and other
polymeric parts, if there is any improvement at all it will not take long
for some other expense to pop up that will more than negate it.
(Fuel leaks or stoppages probably the most likely, paint damage right up there.)
Then there is the fire/explosion hazard. Acetone boils at a bit over 100°F
and makes lots of vapors below that temp.
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George Downs Bartlesville, Heart of the USA!