I was there from April 15 to 18th this year and had an incredible experience. It wasn't hot (in fact, locals complained it was a bit too cool ... but as New Englanders, we didn't mind.

).
We rode LOTS of times, with little to no wait ... we even walked onto Dumbo and rode w/ emtpy elephants (!) this was on an early admission/toon town madness day. Most people in Fantasyland moved onto Toon Town when it opened to ticket-holders-only and we didn't.
We did the raft ride in California adventure first thing one morning and rode FOUR consecutive times w/out getting off ... nobody was waiting. After that I sent hubby and kids to California Screaming for a 20 minute wait, and I walked back to get fast pass for Soaring (the wait was only 30 mins, but this guaranteed us a spot an hour later) ... after Screaming, we did the Dream presentation (Whoopie Goldberg movie), had a snack, and used our fastpasses to walk right into Soaring.
According to a book I read, the week before Easter and the week after Easter are very busy. Then things slow down until about a week before Memorial Day. Our experienced seemed to follow that theory. Easter this year was 4/8. We arrived late afternoon Sunday the 15th and the park was opened until midnight. We debated not entering hte park, but we wanted to see fireworks so we did. We did see some long lines to have 'ears' personalized, and on a few rides ... but not bad. Sadly, fireworks were cancelled for wind.
On Monday ... the crowds were gone!! The cast members were commenting "yay, spring break is over", and everybody was in a good mood.
So ... if you are looking for a spring time visit, I can't say enough about the week that starts the Sunday after Easter.
The only downside ... the parks close earlier (for us it was 9pm) when they aren't busy. But really, we had plenty of time to do everything we wanted to do.
As for closed rides ... Splash Mountain and Tom Sawyer's Island (and the ride to get there) were closed for refurbishing, but they had been closed during the peak 'spring break' time too. Sometimes refurbishment is necessary ... and we could actually see work being done on the island.