Ahh the wheels, they are great, my japanese friend had one of them, worked well in my favour, I got to wheel his backpack and he carried mine hahaha. Also more convenient if planning on catching subways etc, otherwise you get squashed and liable to fall over backwards (not so sure if this would happen in Japan though, Koreans just dont know how to wait).
Yeah I think wheels would work best in Japan.
Off topic, but when we were backpacking through Cambodia there was a group of american girls and one of them had all her expensive suitcases, like perhaps she had thought 'There is no way I am taking a BACKPACK' but she was having the worst time, there are so many holes everywhere, it was wet season and the majority of bridges and plank walkways have boards missing... wouldnt dream of trying to navigate that situation.
Back on topic: Are the japanese transport cards for both Buses, and trains? Also can you pay road tolls on them too?