I have gone the past 2 years in March...in 04 we went March 10-17th..weather was good , cool in the morning and evenings, but we went swimming, wore shorts, and had a nice time...I think just 1 rainy day. In 05 we went the 20th-30th...hotter, only cool 2:30 am at MK!!!

, went to water parks and swimming every day. There might have been a 1/2 day of rain, but I don't remember one. I love March!!!
I didn't know where you are from so that might make a difference, but if you are in the NE or any other cold area, March in Florida is great compared to home
Just be sure to wear layers, and pack a pair of pants and jacket(sweater/sweatshirt) or two. The other great thing about March is around the 10th they start having longer park hours, so there's more time to do everything. Hope you will love March too!!!