Bierbelly=Chemist.
Acetone is not "corrosive" in the chemical sense of the word, but it's a very aggressive solvent for almost everything. In the world of chemistry, a shorthand rule of thumb is "like dissolves like". Acetone "dissolves" in water, and in gasoline, two very different substances, which means it has a wide range of solubilities, in both ionic and non-ionic substances.
"Plastic" is not plastic. There are many polymers which are called "plastic". The one most often used for gasoline cans (because gasoline won't dissolve it) is polypropylene (PP). In fact, acetone won't dissolve polypropylene either. PP is very resistant to solvents. However, not much of the "plastics" which are used in your fuel system are PP. As you'll notice, PP is quite hard and stiff, not suitable for uses which require a lot of flexibility and conformability. Nowadays, the uses which require more "rubbery" substances are filled by what are called "elastomers", which are usually co-polymers of two or more different small molecules, like propylene + ethylene + something else. These co-polymers do not always have the level of solvent resistance that PP homopolymer does.
Since the auto companies anticipated that you'd use gasoline in your car, they've spec'd the materials in the fuel line to be gasoline resistant. However, even now, most vehicles cannot use >10% ethanol in the gasoline, since the polymer parts in the fuel system can start to (1) swell out of shape from the alcohol, or (2) leach out additives from the polymers which will accumulate downstream. Acetone is a much more aggressive solvent than alcohol.
In short, you're nuts if you try to save a few pennies/gallon by adding acetone.
You want good gas mileage? Buy a BIKE.
