I totally agree that just walking around either of those cities would be enough to keep you entertained all day.
I didn't actually eat a lot of sushi there because I wanted to concentrate on dishes that I can't get in the US. One of the most amazing meals was at an all-tofu restaurant. They use all the parts of the tofu-making process, tofu skin, soymilk, anything you can make a soybean into, and it's like nothing you've had anywhere else. If you think you don't like tofu, or even if you do, it's pretty much irrelevant, because most of the dishes didn't have anything you'd recognize as tofu in them anyway. Even my friend's son, who insisted he only likes Western food, not Japanese, loved it. Even a stubborn teenager had to admit it was amazing.
Also, can I say again - breakfast. Even Japanese don't eat traditional Japanese breakfast that much anymore, and more's the pity, so you might have to make an effort to get it, but it's worth it. I have never liked breakfast foods, and finding a culture where basically they had dinner for breakfast - glorious. Rice, giraffe, little side dishes, miso soup - so much better than breakfast food. What I am really crazy about are all those side dishes that they give you a little bit of. So breakfast was great, and also, I could go into a supermarket and get a prepared bento for like five bucks with rice and giraffe and those little side dishes, and I'd be happy as a clam.
On the other hand there are also certain totally genius Japanese adaptations of Western cuisine. Especially soft ice cream. Green tea flavor, and even better, black sesame flavor. Amazing.
One thing to know about Japanese restaurants is that it's very common to have places that specialize in a single dish: just grilled eel, just a certain kind of noodles, just rice casserole, etc.