High housing costs have prompted some in the middle and upper classes to rethink what they value – and be willing to give up the rest. SEATTLE; AND LOS ANGELES — When Shawna Nelson leaves her office in Seattle’s suburbs, she does what 28-year-olds often do: dines with friends, goes out dancing, or sees a show. Sometimes she hits her swanky gym. But at the end of the night Ms. Nelson always returns to Dora, the dusty Ford Explorer she calls home. In the back, where a row of seats should be, lies a foam mattress covered with fuzzy animal-print...