Great tips and great discussion.
Naphtha may harm the plastic.
A few more tips based on customer experience:
"Dawn" and "Fairy" dishwashing detergent in warm water work well, too.
Do NOT use any thinner containing acetone, acetate, or methyl ethyl ketone (MEK). Acetone will attack acrylic plastic and damage it. Acetate is found in acetone-free nail polish remover. Acetate and MEK can cause a crystalline powder to form on the surface, even after painting, which is an annoyance to remove. The following chemicals may cause crazing, cracking, discoloration, or dissolving of Frosted Detail acrylic plastics: Acetic Acid, Acetate, Acetone, Ammonia, Aromatic Solvents, Benzene, Brake Fluid, Butyl Alcohol, Chlorinated Solvents, Disinfectant, Ethyl Alcohol, Kerosene, Lacquer Thinner, Lestoil® Cleaner, Lysol® Spray, Methyl Ethyl Ketone, Naphtha, Pinesol® Cleaner, Sulfuric Acid, Turpentine, Toluene, White Cap® Cleaner, and Xylene.
After a good UV treatment, to smooth larger Frosted Detail surfaces, or to get into nooks and crannies that are difficult to reach, careful use of an inexpensive "air eraser" emitting common household baking soda can help smooth surfaces and remove any unwanted "frost" without harming detail. Air erasers, like an airbrush but much cheaper, can be found on Amazon.com. Models by Harbor Freight and Paasche are popular.