I agree with Marko, it is half improvement, half hobby, half money saving, half education, half exercise (but not half math)
Add to that our van is still way, way, way, way, less than the price of a house, but very near exactly what we want, and it is a good way to spend my time. I doubt very much that we could get what we want to do, or test, from the marketplace, as we can afford to try and experiment on ourselves, and make mid course corrections. Sure beats sitting in front of the tube!