What is stealth wealth? In financial circles, it's not a new concept. The Millionaire Next Door, a classic book we read back in the late 90's, exemplified the idea by pointing out that many millionaires are unassuming. And they're millionaires in part due to their simplicity of choices for housing, cars, etc. Physician on Fire wrote an explanatory post about the concept in the early days of his blog. To us, the term wealth has rich meaning - both literally and figuratively. It's not just …