To my mind, inspiration comes from flexibility, i.e. when you can choose to change environment as you please. A mid-size city is ideal for that, since you can have times in the city and off the city, that change your perspective. If you live in Tokyo, you just cannot do that, and you are stuck in a world that is very different from everywhere else, and out of touch with a lot of what most people consider "reality".
Disclaimer: I live in Japan.