I'm personally a firm believer in taking kids whenever you want to go. This is how we like to vacation, so instead of going to the beach, we go to Disney world where they can ride almost anything at any age. I love it, and my kids had a blast. My now 5 year old has been twice, once at 2.5 (free before three!) and once a month ago for her 5th birthday. She currently remembers some from her first trip, but I'm sure that will change as she gets older.
For us, it's a magical experience and I don't know how much longer she'll believe in everything. She's way too smart and always trying to figure things out.
My son's first trip was a month ago. - he is 18 months. I do not care one bit that he won't remember anything.
I do like the logic I've seen here before that if you only do things when your kids will remember them, why bother taking them anywhere before they're 5 or 6?
I will forever remember my then 2 year old bouncing with tigger, checking to see if chip had been brushing his teeth, and wanting to ride the carousel nonstop. It was awesome.
This last trip, she got to do bibbidi bobbidi, loved the magic carpets, met as many princesses as she could find, decided she was brave enough to ride mission:space with daddy and yep, she was the pilot! She then went on test track and was so proud of how fast she drove the car!
Even my 18month old had fun, and it was awesome time for us as a family. My kids running around on the balcony at contemporary while the fireworks were going off - priceless!
If your trip will be one and done, sure, maybe wait, but if you think you'll probably go back, I would just go when you can. But remember, it's almost never going to be the perfect trip, tantrums can be thrown by a person of any age, and you'll never see everything, do everything , or remember everything.
I wish you a magical trip whenever you do go! It will be awesome no matter what!