Interesting about craigmillar castle. I worked in the parks department of te council when they were securing the funding to do what they've done so far, but not seen it since I left. There were a fair few amazing little bits of track hidden away a few years ago, but its not somewhere I would have hung around back then, unless you were into burning out cars and mopeds. There was some interesting stuff around Edmonstone too but not been there since worked for the council either, I think it is all handed over to developers sadly. Some amazing trees in there around the ruins of the house.
PHRP do a pretty good job considering the resources they have, ie, nowt, and the enormous number of park users.