Can't help with either of the main lines of enquiry (e.g. 1, I haven't got a DVD of the plays and 2, I've no idea, after 20+ years, about the clothed/unclothed debate):

But I just thought I'd mention there's lots of interesting background detail, anecdote and general context about The Mysteries and the Cottesloe Company that created them in the book 'Impossible Plays' by Jack Shepherd and Keith Dewhurst.

Someone on concertina.net tipped me off about it, I thoroughly enjoyed the book and it brought back some happy memories of The Mysteries and Lark Rise, so I'm passing the favour on ...