Ok, so here are my thoughts based on our previous spring break trips, and one "week leading up to Christmas" trip. The one year I thought, "Oh, Easter is April 20, and our spring break is the last week of March, WDW shouldn't be as crowded as it has been in previous years." It turns out when Easter falls later in April, Florida schools have spring break in March. We are actually seeing a similar thing in the schedules in the districts in Ohio right now. That one year, 2014, there was a day we were at Magic Kingdom that I'm pretty sure the entire state of Florida was there. It wasn't even a phased closing day, but we left for the afternoon and came back in the evening. There were cars parked on the lawn back by the racetrack in the TTC parking lot. That is the only "miserable" day I can recall out of 3 years of Spring Break trips. I'm actually happy our spring break is April 13-20 this year! I've been there on a day in December last year that I think someone said had 80,000 people, where they were directing people away from the hub 30 minutes before HEA, and even that day didn't seem as bad.
Having said all of that, here is my experience and how we personally handle it.
Before your 180 ADR window, make a rough plan of which parks you think you want to go to each day, which rides/shows/activities you and your family may want to do. We personally avoid the parks with EMH even if we've been eligible for them.
Make ADR's at 6am 180 days out. Additionally, we have had much better luck doing lunch reservations, and trying to go to lunch at 11:30 or as soon as the restaurant opens for lunch. The times we've booked dinner are the reservations where we've waited 45 min or more for our table. It's less stressful to be seated right away, have your order taken right away, etc. Plus, assuming some parks open at 8am (MK and AK tend to during Spring Break), you'll have been pounding the pavement for 3.5 hrs at that point anyway, and the parks will start getting crowded by 11:30.
Make FP as soon as your window opens. We typically do FP 9:45-10:45, 10:45-11:45 and 12:30-1:30.
The week before your trip recheck the park hours. We've experienced the MK hours changing to an 8am open from a 9am open days before our trip. Same with AK. I wouldn't be surprised if this year HS opens at 8am.
For us, rope drop is super important on Spring Break. My kids also naturally wake up at 6:30am no matter what. Each night check the park hours for the following day. The parks will often start letting people through the touchpoints 30-45 min early depending on the park (I believe MK may actually be an hour early now). So, if you want to do rope drop, count backwards from official park open. Determine what time you want to be in line, even if you aren't at the very front (also consider time to go through security before reaching touchpoint line). Then figure out what time you need to be out the door in the morning to arrive and be in line by the time you want to be in line. I have to do this, because every night my DH asks me, "What time do you want to leave tomorrow?" So I've had to work out this process now so that it's almost down to a science.
We ride as many rides as we can during those first couple of hours, then use our first fastpass near the end of the fastpass window. Then move onto our 2nd fastpass ride. Then go to lunch. Then 3rd fastpass ride. Then fight our way back to the front of the park through the walls of people looking at their phones and maps and fighting with each other over what ride to do, leave the park, swim in the pool and take naps. My point being, we avoid the most stressful and hottest part of the day. We return around 5 and stay til park close.
For evening shows, I'd consider booking a meal package or dessert party that includes a designated seating area. We did the HEA dessert party with plaza garden viewing at Christmastime, and as they announced that the hub had reached capacity 30 min before the show, I could not have been more grateful we splurged on that.
Lastly, we drive our rental car to all of the parks.
So, this is our "survival" plan each year and how we tour the parks. We kind of like the busier times, because the parks tend to open earlier and stay open later. We also haven't really been at a "slower" time. I know this is a lot of info, but it's what has worked for us! Good luck, and maybe we'll see you there!