I was worried a bit about going during Spring break (ours is the week leading up to Easter). However, from recent posts it looks like there may be some advantages. It looks like most, if not all, of the construction in DL may be over. Also it looks like those days may be blocked out for AP s. So not as many locals. I expect crowds. This isn't our first trip, so there's no need to do everything. We will have 4 days, so that should help.
Here is what you should expect looking at the blackout calendars:
DCA: Packed the entire week because Cast Members can sign into DCA that week and given how much they have been blocked this year from signing people in, they take full advantage of it while they can. Add in most passes aren't blocked out the 26th through the 29th and it will be busy.
Disneyland: Busy 26th -29th because most passes are available.
Both parks are going to be packed on the 30th because not only is it Good Friday (which more and more local businesses are giving off), it is also Ceaser Chavez day that day, so it is a state holiday, which all schools get off.
Chances are April 1st will be the least busy day of the week, with March 31st being a close second, but the other days of the week, expect very high crowd levels. When looking at crowd levels, it is always wise to consider cast member blackout dates in addition to passholder blackout dates. I also just looked at the crowd calendar on isitpacked.com and quite literally they predict:
"Forget About It" for the 26th through the 29th
"Yup It's Packed" for the 30th
"Yup It's Packed - Best Bet" for the 31st
"Hey, It's Alright - Best Bet" for the 1st
And really their predictions are fairly accurate, which do happen to coincide with mine, although we have different rationale behind why.
Also, weather may have been factor in keeping crowds lower last year.
I am not saying you can't have fun on these days, but you should have realistic expectations on crowd levels.