Flying Fish is tied for our top restaurant that is on the dining plan (along with Citricos). We actually ate there twice on our last trip, once as part of the Chef's Wine Tasting Dinner and once off the regular menu. If you are looking to treat yourself to a great dining experience and you are a bit of a foodie, deffinately check out the Chef's Wine Tasting Dinner. It ran for us about $158 per person including tax and tip. This is served at the counter that looks into the kitchen, where you can chat with the chefs. There is a different counter where you can sit if eating off the regular menu (this is the bar counter which is next to the kitchen counter).
We are also big fans of Jiko. Since you are staying at AKL, have you considered looking into the Wanyama Safari? This is another experience we did this past trip and I have to say, it was the best experience we have had at WDW. It runs about $190 per person (including tax and tip) but we felt it was worth every penny. First, you meet with your guide and head out on the safari that goes through all the savannahs at AKL. The animals get so close. You hear all about the animals, how they are cared for and even some of their individual habbits both as a species and as the individual animal itself. After about 90 minutes or so out on the savannahs, you are taken for an awesome feast at Jiko, which also includes wine pairings.
I think no matter which way you go, be it off the regular menus at Jiko or Flying Fish or either of their special experiences, you are in for a great dining experience. I don't think eating at Sanna, Boma and Jiko all in one trip is too much, either. The menus at all 3 are quite different. We ate at Jiko twice (once as part of the WS), Boma three times (twice was for breakfast) and once at Sanaa and we didn't feel like it was overkill at all (our trip was for 11 nights).