"Is it worth me scouting for them or are they likely to have been farmed out of existence?"
I've seen many hut circles on Dartmoor. Most of higher land is just grazed, so much remains of the old field systems and hamlets.
It is one of the most humbling and mind-bending experiences to stand in the doorway of some Bronze Age dude's gaff.
Grimspound sticks in my memory as being a particularly fine example.