I don't have any experience with JRTs specifically, but I definitely have years of experience with breeds that have that difficult combination of high energy and high intelligence. Namely Border Collies, Australian Cattle Dogs and Labs - also breeds that can do a lot of damage when they get bored.
My best advice is you need to run them hard to get that energy out and find something they enjoy so it keeps their interest. Tennis balls and those launcher arm deals have worked wonders for me (into a lake if possible in the case of the Lab). Also take them out of runs/walks or hikes.
And don't give up on the crate training, either - in my experience having crate trained dogs is important.