As a MD user myself, aside from Lance's magical find at the end of series two, it's been very much my experience of finding bits of fencing wire and staples, ring pulls, the odd horseshoe and tractor parts. I've not found a single coin yet let alone a hoard, but did find some when I last used a MD when I was in my early 20's :-).
I've recently teamed up with a pal who detects with a MD and wait for it - dowsing rods!! The rods come out if the landowner is looking for drainage pipes and the likes and I've been impressed by his finds, but that's another story.
And that has made me wonder if the success of Detectorists could be replicated by another station doing the same type of thing but with dowsing as the main theme? Could it work? I think it could as there are a lot of similarities.