Our 1st trip to DL is set for June 17-23, so we're going to miss the opening of Pixar by a day. My kids are thrill nuts, so they're going to be very disappointed not getting to ride the coaster or ferris wheel. First, will Toy Story and Little Mermaid be open before the rest of the area? Secondly, would you pay $1,000 to change flights to go at a later time, or simply take a day to go to Knotts Berry Farm and ride the coasters there to make up for what we'll be missing at California Adventure?
Go to Knotts, buy some Fast Lane passes, and you can knock out all the thrill rides by early afternoon and still go to Disneyland in the evening - close. Or take the whole day there and enjoy a more leisurely pace.
If your kids are REALLY into thrill rides then take the loooooong drive (due to traffic) to Six Flags Magic Mountain. Buy the Flash Passes - they can be pricey. My kids are 20+ and we've made the drive from Anaheim to SFMM several times. Long drive - but worth it for us.