Unfortunately, Home Depot doesn't deal in scrap copper. Well, even that's debatable from a plumbing point of view, but what they sell is fashioned into a useful form - pipe. And fact is, they probably bought that stuff months ago so it's priced based on its cost (and on what us home-improvement drones are willing to pay). If I were a plumber, I'd be more tuned into prices or I'd be using that plastic stuff that they seem to be pushing now.
On a happier note, drywall board is down from what it was a couple of years ago during the building boom. Not that I'm going to stock up on it or invest as if it were gold!
As for gold, I'm holding what I've got. I'll buy more if the price drops quite a ways.
Got to add, if the price spikes way up, I may sell a few ounces to feed the irrational market. Cash is still useful, too.
However, you should the great deal for scape goats down at our farm store. Prices are WAY down for new, virgin scape goats.