St Just must have changed since we last tried to call. We used to visit the cafe when we were in the area but after they rebuilt the terminal there didn't seem to be anywhere to just get a cup of tea and a bun. We'll be in Cornwall in a few weeks so might give it another try.
Old Warden has probably got a similar big cheese to the one that abolished Friends of Duxford and combined it with Friends of IWM. I found an FOI request online a while ago and it said that of around 5,000 FoD members, 800 signed up.