If there are certain attractions or restraunts that are must-sees, make your firm plans for those, making reservations if needed and Fast Pass plans. Try to be in the area around those times.
Other than that, I would only plan for what to be aware of when you are in the area. We were so busy tying up loose ends at work before we left, that my wife didn't have the bandwidth to get involved much in planning. Even with 4 days in the parks, we were resolved to the fact that we would miss things. Keeping it simple allowed us to be flexible and relaxed instead of stressed when things didn't go as planned.
On the day we chose to do the character breakfast at Goofy's, it seemed every kid staying within 10 miles showed up and there was a 45-minute wait. We put our name in anyway and walked around the DLH and got our DD's hair wrapped. After that, we figured, why bother and went on in and did the breakfast at the Plaza Inn. We were pleasantly surprised finding a very quiet time with few guests and lots of one-on-one with Pooh, Tigger, Piglet, and Eeyore. This "unplanned" event lead to one of the highlights of our trip! It' the surprises that are the magical moments (except the 2:30 AM fire alarm at the Westcoast Anaheim).
From what I an understand (DL this year, WDW/
DCL and reading the boards), the people who don't get involved in planning don't because the details don't matter much to them. I've never heard of any troubles when things go wrong. Planning is a great diversion from the anticipation for some people, myself included, but shouldn't take away the necessary flexiblity to have a magical trip.
Good Luck, have a great trip.
UB