I just visited the Huntington Gardens for the first time a couple days ago. Obviously, the Huntington is a renowned museum outside of being a botantical garden, but I couldn't help but feel that a clone of Ghibli Park would fit perfectly with the existing gardens focus on ambiance, exploration, and nature over rides.
(and also selfishly, The Huntington is very cool and it would be cool if I didn't have to travel to Japan to enjoy Ghibli Park)