My DD has seen Spectro at ages 9mos, 3.5 and 4.9. She always loves it. It's a definite must see and I'm sure they'll get a kick out of the characters and the lights. Plus it will be a new experience for them.
As for Wishes, to try something different since they already saw it, an option would be watching them from the Poly beach (beautiful, and I believe they still pipe in the music) or, if you can splurge, a Fireworks cruise.
I'm pretty sure they'll love both.