Castle in the Sky has never been released in the US to my knowledge....I do know of some who have it in the orginal Japanese. The 1986 release was in Japan.
Disney's been sitting on this one for a long time...there's a preview for it on one of our videos (possibly Kiki's Delivery Service? which was first released here by Disney in ....oh, the 90's sometime I think). All three movies are being released at once now...Spirited Away, Castle in the Sky and Kiki's Delivery Service. All were done by Hayao Miyazaki...considered by many to be one of the greats, if not the great of Japanese animation.
So anyway, judging by his other movies, I'm sure this one will be well worth it.....but to decide for yourself go rent some Miyazaki (My Neighbor Totoro, Kiki, Princess Mononoke) to see for yourself. His work does vary a lot though....some of it is very suitable for young kids (totoro, kiki) and some of it is very, very mature (Grave of the Fireflies). I'm assuming the new releases are all fairly kid oriented.