I would go by what Disney thinks is Spring Break and you can tell that by looking at park hours and entertainment. When they both go to maximum or near maximum conditions you can tell that Disney expects extra Spring Break crowds. Maximum hours is 8AM-Midnight at DL and max entertainment is daily fireworks and Fantasmic, and parades. Next March Fantasmic will be down so will not be able to use that as a guide.
In recent years DLR has maxed out hours around mid-March until mid-April. So you will likley be ahead of that. To see past years check this link:
"Historical DLR Park Hours, Entertainment and Refurbs" -
www.disboards.com/showthread.php?t=2291124