My husband and I know good sushi too, and would love to find a decent sushi restaurant in WDW. We were in Epcot for Food a Wine a few years ago, and had some sushi rolls at the Japan food and wine booths. They told us it was the same sushi they serve at tokyo dining (don't know if anyone can confirm this) but is was really BAD. Like grocery store sushi or worse. So I have been scared to make a reservation there or at Kona. So the options left are California Grill ($25 for one sushi roll) Morimoto Asia, or Kimono's. Any of those would probably be good and close to what we get at home. But none of those options really work with the dining plan I believe.
Even at Tokyo dining or Kona, I'm not sure how sushi would work on the dining plan. Using one credit for 1 sushi roll would be a total waste if that's how it works.