Wealth is created by taking things of low value, and making them go into higher value. You already seem to know that since you get stuff that's sold on the cheap, and go into areas where the demand is immune to a higher price. Its the same principle Starbucks uses to scout out good locations for their franchises. Smart move.
I would say that something that enough people don't do that has a potential for making pretty good money is fixing electronics. Most people don't bother changing their ipod battery, for example.