SOME FOLKS achieve a Zen state by meditating; others run. And a few do so by lovingly detailing their cars. “It’s something I look forward to every week,” said Jacquelynne Tyner, a student at Cal State Monterey Bay, of the two hours of zealous, focused cleaning she lavishes on her 2006 Mini Cooper S Convertible. “It’s very manual, very therapeutic.”

Ms. Tyner is among a growing number of car-care hobbyists who take the craft to new levels—thanks to cleaning tools and materials once available only to pros. Detailing a car...