To be nitpicky, (and slightly tongue in cheek), would "treasure hunter" not be a more appropriate term than "metal detector enthusiast"? I assume if there were a better tool for finding buried treasure, they'd happily ditch their metal detectors.
I think "treasure hunter" is more likely to conjure the image of someone who'd pawn off an artifact to someone else. Like the people who busted into Egyptian tombs over the centuries.
If they were after finding treasure, they would be better off buying lottery tickets. Metal detecting finds are more likely to have archaeological value than monetary.