I like Warp's post. I've already spent way too damn much on this hobby, and as hard as I tried to "do it right" the first time, that's pretty darn impossible for a newcomer (few years ago). Without the foresight to see that I will continually want to upgrade, even though my jaw hit the floor so many times in the beginning, I am now trying to embrace the idea of DIY as best I can. I won't ever be able to DIY an AV processor, amplifier, or projector, so I better take my chances when I can on speakers, subs, and the like.
Warp is also right about the things you learn. So many people in this hobby have a lot of knowledge in things engineering, physics, paints (and how to apply), insulation (and how to apply), woods (and how to work with), fabrics (how to affix/attach, where to buy), and oh yeah 9v battery tests, multimeters, optics or light transmission, human perception both visually and aurally, list goes on and on . . .