We went last year with our girls, they were 5 years old and 16 months old. "Worth it" is always subjective, but we had a great time. It ended up being more crowded than I thought it would be for an end of Sept party, so we didn't get to do as much as I'd hoped, but honestly I felt like the parade and fireworks alone are almost worth the ticket. Definitely the best fireworks display I've ever seen. We also had an amazing interaction with Alice and the Mad Hatter - we dressed as Alice (DD5), the Queen of Hearts (DD1), and Tweedledee & Tweedledum (me & DW) - and got to meet Queen of Hearts. I would like to go back again when they're older, but knowing that will be difficult with school schedules, I'm glad we went when we did.
My one piece of advice - do not go to a park in the day time on your party day. We had a late breakfast at 'Ohana, then DW took DD5 to play in the arcade while the baby took a nap in the room and I ironed/prepped our costumes. We got a pizza from the food court for an early dinner in the room and got to the park around 5pm. We were able to stay through the 2nd parade (not the original plan, but we missed Alice on first stop and had to go back, so we ended up missing the 1st parade) and no one had a meltdown! My kids are more night owls than morning people anyway, but I think resting that day helped everyone stay in a good mood for the night.