We've done the deluxe plan twice so far, with a third go at it coming up next month. My kids were 9 and 6 the first time, and 11, 8, and 1 the second.
We do a lot of signature dining. Read Disney's dress code for the signatures and you'll see it really isn't dressing up in any sense that would annoy most kids. My DH & son wear kahkis or black slacks instead of jeans to the park that day (though jeans are permitted), along with polo style shirts instead of the usual tees (tees are allowed as well). My girls wear the jumpers & leggings or capris that they wear every day in the parks, and I wear non-denim capris and a cute top or a blouse over a tank. Very casual, still park and weather appropriate, and yet nice enough to put us in the middle of the pack as far as how signature restaurant patrons are dressed - you'll find some in jeans, tees, and
crocs and others in evening wear. The signature kids' menus are so much better than the standard 1 credit kids' menus that my bunch really appreciates having those meals planned.
I do feel that three sitdown meals per day is both too much food and too much time away from park touring, but you don't have to use each and every credit for TS for the plan to be worth having.
The general rule of thumb for the plan from a dollars-and-cents standpoint is 2/3 of credits used for table service, so you could plan a character breakfast and a nice dinner every day and come out ahead even without signatures or shows.
Also, keep in mind CRT and the Brown Derby (with or without the Fantasmic package) for some very casual 2 credit meals that take no travel and less restaurant time than the other signatures.
In our deluxe planning we book two meals per day. Some days it is a character breakfast, some days a TS lunch. We have a lot of signature meals, but we also leave a couple credits unplanned to grab CS or order room service/pizza delivery if the mood strikes. And we don't miss snacking, as a previous poster did, because we use our snacks to fill in between our ADRs.
Our days on the deluxe plan mostly look like this:
9-12, park time
11:30-12:30, lunch (we've found that early seatings, 11:30-noon, generally make for a quicker meal than later lunch times - we've had very few lunches take longer than an hour, but I try to book the first lunch seating whenever possible)
1:30-6:00, park time
6:00-8ish, dinner
We don't catch the evening shows every night or even every trip - we always see Wishes but sometimes skip Illuminations and generally don't bother with Fantasmic unless we have a dinner package. That makes it so that we don't have to take breaks. If we take a midday break it is because we're going to evening EMH that day, so the time out of the park in the afternoon is offset by the extra time after dinner.
Sometimes instead of lunch we'll have an 8-8:30 character meal and then just have snacks during the day to tide us over until our dinner ADR. Doing character breakfasts became kind of addictive for us because my girls collect autographs and we can skip so many in-park character lines just by adding one Princess meal and one Mickey meal!
It does take a lot more planning and forethought, but I absolutely love the deluxe plan and can't see my family going without it at this point in time.