Hi there. Saw your post and wanted to let you know that we were there last March and it was not terribly crowded. My DH works at Indiana University and our Spring Break always includes St. Patty's Day, the 17th. Last year that meant the break was early, the 2nd week in March. The crowds weren't bad at all. We were able to make some last-minute dinner reservations and get lots of fastpasses at the parks.
It seems to me that the Spring Break action really begins in the last half of March. I did not feel that it was me and a million crazed teens, either -- the crowds were the normal Disney mix.
Hope this helps.