They may not yield old coins but if you dont mind digging newer money these sites can be gold mines when it comes to lost change. Save it all up over a season of detecting and then cash it all in. Who knows you might have enough to get that new rifle you HAD been saving for.
There is alot of lost change out there not to mention jewelry and other valuables.
I have found Bracelets, Watches, Rings, Earrings, Pendants, Gold Chains and Medals just to name a few. You would be surprised at what people lose.