One thing they are good for: That odd battery, cable, or connector you “need right now” on a Sunday afternoon.
In their early days you could purchase kits (Heathkit) to build your own electronics. They could rise again if they had the right vision and a way to execute it. Explore some of the cutting edge offerings. Build your own NSA foil, for example. Tin foil hats, too.
For any of those, I've recently found Battery Plus stores, which seem to be popping up in many places. Very convenient, they always seem to have what I need no matter how esoteric, and have decent prices.