Usually I decide on the resort and dates - book my room and make my ADRs...and that's about it. I usually have a general plan on what parks I'll go to on what days - based purely on how I feel and ADRS - not EMH or crowd levels or such. Plus I always get park hopper so if I can swtich parks during the day if I want.
I like to go to MK the day I arrive and I do so no matter what other sources might say about crowd levels.
Since I've been to WDW so many times I really don't fell like I'm missing out on anything if I don't do all my favorite rides. I've been on them before and will go on them again. If a line is too long I may use fast pass if it's available to just decide to skip it.
I do like to research what's new and happening during the time I go so I am aware of things I would like to do. But I find the more I go to Disney the less specific planning I do. But I do agree it's fun to research and think about the trip prior to going.
We're taking DS for the first time this year and he will almost be 2 when we go. I find I am planning more this year, but most of it is making sure I have what I need for DS to make it an enjoyable trip for him. My planning is mostly what stroller to take, what to pack in the diaper bag, ordering supplies (diapers, snacks, etc) from a grocery service, planning ADRS to work with his eating schedule and picking restaurants that offer food he will eat and like.
Plus I am staying at a
DVC for the first time this year (we rented points from a friend) and since DVC doesn't have cleaning services every day(unless you pay dearly for them) I want to make sure I bring what I need. Plus I will have a full kitchen and a washer and dryer in my room so that adds possibilities.
I like some spontenaity during vacation and the freesdom to do what works best for my traveling group at any given time.