Well that certainly explains your frustration.
But doesn't your scenario sort of ring true with the statement that you disagree with? You seem angry because she gets on you about buying car parts. Or painting a car or whatever.
So because she's not happy you aren't happy in that instance. Honestly if you think about it, it is a pretty true statement.
And I agree if you are providing everything then you should be able to get what you need if affordable, I don't see the problem.
My wife doesn't work either, when I get something she doesn't complain, often, lol, but I have just the opposite problem when she needs something I have to make her go get it, or get it for her.