We have done a couple Spring Break trips.
The crowd calenders were rating the parks at 9 and 10.
Honestly the worst part of the trip was the drive to and from WDW on I95. Should take us about 10 hours but it took over 12 and it was speed up, slam on brakes, speed up, slam on brakes bumper to bumper, white knuckle driving.
We get up early to hit the parks and to go which ever park has morning EMH. During Spring Break some of the parks were opening at 0700. And we were there at rope drop.
We would get to the parks early, then get out around lunch time when the crowds got crazy. We would eat lunch and go to the pool for the afternoon. Tis better to eat at the resort for lunch to avoid the crowds but if you are at RD at 0700 you will likely be eating at 1100 in the parks which means you miss the lunch crowd.
We do not stay all day in the parks. If you do then the Spring Break crowds could be a problem. Honestly we were able to work around the crowds. We noticed them compared to our October trips but it was doable.
On one of the trips we happened to be at WDW at the same times as the DW's cousin's family. They had a horrible time because they could not use EMH since they were staying offsite and they did not know how to avoid the crowds. They got to the parks around 1000 which is what many people do, so they spent quite a bit of time waiting in line. When they were walking down Main Street at 1000 we had been at MK for three hours and were at the back of the park thinking about going back to the resort for a break and swim.
Spring Break is very doable if you do a bit of planning. We prefer NOT to go during busy times but you gots to do what you gots to do.
Later,
Dan