Another reason was that, even when only estimating spending, as a kid I tended to over-emphasize "conspicuous consumption" and gadgets: assumed the people with bigger TVs, new game consoles, better cars, etc. were wealthier. What I massively underestimated was the cost of "nice" vacations (esp. compared to relatively minor items like game consoles), so it was really the people who liked to travel a lot who spent more, but I never saw their spending happen when I was around.
edit: To add one more confound, I think I also put too much emphasis on "class" associations: I assumed parents working blue-collar jobs made less than white-collar, which was not always true, esp. when you took into account that some blue-collar families had 2x incomes.