Well I think it grows on itself.
We went when DS was over one (note: I'm talking
disneyLAND here), and it was fun.
Then we went the next year, and it was great fun. We didn't think he remembered it, and then a few months after we got home, he had a language explosion and just started talking and talking about it. He can tell us things we had forgotten about the trip.

So not only did he have fun while he was there, he continues to have fun just thinking about it!
And of course there's no way to know if he remembered anything from the first trip, since he didn't have the language to talk about it until well after his second trip.
This upcoming trip, he's been excited about it since April or so. When he's afraid of monsters, we talk about changing the room into Disneyland, and he enjoys imagining the rides he remembers, and picturing the characters he has since learned (this coming trip will focus on characters a bit more, while the last ones we just avoided it all). He talks about when we go, and we can help him to sleep by talking about how he will be able to dream about Disneyland the sooner he falls to sleep.
If this upcoming three-year-old trip goes even half as well as I hope it will, it will be impossible to determine how much of the fun came from what happens, and how much of the fun came from the anticipation based on his last visit(s).
I think it builds on each visit. If you want to visit, and you CAN visit, now, go for it. Don't make it ALL about her, be sure you'll have fun, too, so the trip isn't totally ruined if she doesn't like what you thought she would like.
Lastly, I just LOVE that this is DS's third visit in 3 years, and it's at long last his first visit where we have to pay to get him in the gates.
