Definitely go! We took our daughter when she was a month shy of her third birthday. It was great.
Take pictures and some video. We were surprised at how much she talked about it even after a year or so. She loved to look at the pictures and videos. We taped some of the rides and fireworks/shows. She would constantly say, " I remember when ..... ".
We went back just this month, she turned 5 at the end of Spetember. She would sometimes comment on how we saw this or did that the last time we were there. Plus we were able to go to things we couldn't before. Then and now it was a great time with great memories. When we met Mickey at the Toontown fair, we waited in line, when it was our turn, she ran up and gave him a big hug. I have it on video and can hear the teenage girls behind us saying, "Oh, isn't that so cute."
We took her to the princess breakfast in Cinderella's castle, a huge hit. Many of the cast members were great, we bought her some mouse ears. Some of them greeted her with, " Hello princess " or " Hi mouseketeer ".
Only you can judge how your child will react to the characters, walking some, the attractioins, etc. If you go, definitely bring or
rent a stroller. It will make some great memories for you and her.
Also a side note, if it still hasn't changed, when we went in 2002, children under 3 did not require a ticket, a big savings depending on the length of stay. We did use the baby swap to ride some rides she couldn't.