Actually, it is Spring Break for many school districts. Us, for instance!
We'll be there, and I know several other families from my area who will be there, too.
Plan on crowds, take your time, use FastPass, go left instead of right, squeeze in an early afternoon break from the crowds if you can, take advantage of attractions with very short waits even if they weren't part of your plan... We've gone several times during Spring Break, and haven't found the crowds to be deal breakers using these strategies.
And it's important during crowded times to make PS arrangements for any meals in sit down restaurants you don't want to miss.
For crowded times, I usually make a plan that tells us what park we're headed to on each day. Then I'll often make either a lunch or a dinner PS somewhere. That gives us a good starting place... my philosophy here is "Now we have a plan. If anyone has a better idea, we'll do that instead." But it does give us direction, and we don't find ourselves out in the cold if the restaurants are booked solid.
The weather can be unpredictable- we pack everything from shorts and tank tops to jeans and sweatshirts for March. If you bring a light jacket along, you'll be able to layer to get you through days with cool mornings and warm afternoons.
Wear your lime green, and say "Hi" if you see us in the parks!