I skimmed over everything you guys just posted here and I keep seeing Vallejo thinner posted time and again. You don't need all this high priced crap. Look - nail polish cleans up real well with acetone or even with xylene. However you wouldn't want to put the latter on plastic because it will mar. Acetone is a solvent based alcohol that flashes off quickly and dissolves in water. It is compatible with most paints as a solvent. But regular rubbing alcohol (isopropyl) will thin paint as well as remove it if it's acrylic. No need to worry about solvency or compatibility. It dissolves and doesn't leave a residue. Neither does acetone. When you rub plastics with it the surface dulls but does not dissolve into a mess. However acetone is expensive and toxic to your nervous system when inhaled on a consistent basis.

 Try using 70% or 90% alcohol to thin your paints and practice on scrap. When in doubt - do find out!  Try using different needles and paints and different concentrations on garbage models or spare styrene to get the best out of your paints. I use automotive acrylic primer - much more for less that what you pay for name brand garbage in a small bottle that is no better and costs more. Just spray it into a soup can then into a jar for storage so that you can put it an airbrush. Spray cans don't always atomize the best and stop spraying after a while - especially RUST-O-LEUM brand paint!! I too used to think that you needed all brand name junk just because the manufacturer wanted you to buy their stuff so that they could make more money. Trust experience over hype. I had to learn over a long time that there are work around resolutions to many common problems. I only use thinner when I have to spray a light coat that is not meant to be touched ever once assembled. This goes for doll houses and delicate items that you don't want to handle and need a smooth finish. Otherwise I spray it directly from a paint can (spray paint).