We went 3/11-15 and it was bananas. Absolutely nuts. No FP's available after 2pm, 60-90 minute waits on all the rides in the afternoons. Thankfully the weather was cooler, so it made the crowds more bearable.
We had a great time. But I had very low expectations of getting anything done. We did early mornings and left the parks by 2pm before things got insane. I was pretty bummed that F&G was such a mob scene both days we were there. I didn't really get to experience the festival. We were just trying to avoid hoards of people.
I'll never go during Spring Break willingly every again.