I've gone with my twin 2 year olds - twice! We went in December, 2005, and they were 28 months. We went again this past June, when they were a little over 2 1/2.
Our girls are VERY used to their schedule, so I wasn't sure what to expect. They did very, very, well. We let them sleep however late they wanted to in the morning (which with them meant maybe 7 a.m. - usually closer to 6:30 - all three of my kids think that they are roosters). We very much went at our kids pace (I have an older DS that just turned 7 yesterday). I made a point out of offering food and/or drinks every hour or so, even if it was just a quick sip of water. I know my kids well enough that if they get sidetracked and get hungry or thirsty, they are much more likely to have meltdowns. I made the grand mistake of taking them on POC, which absolutely terrified them because it was so dark. After that, they pretty much only went on rides that I knew were either out in the open or had plenty of light.
My girls did VERY well with all the characters, mainly because big brother is their idol, and everything he did they had to do also. The Pooh's Playful (Thoughtful? I can't remember right now) Spot was great, they really enjoyed running around.
As far as naps, when they were tired they just fell asleep in the stroller. Mind you, if they are anywhere other than their beds at home, they absolutely will not sleep. They don't even sleep in the car! So, the fact that they were sleeping in the stroller was amazing to us.
We used our double stroller, since our girls are so used to riding in it. I tried a harness on them before we went, and they absolutely hated it. Heads spinning around type of hate. Maybe if I'd used it when they were younger it would've been a non issue, but there was no way they were going to wear that harness and be happy about it.
We didn't have the dining plan either time that we went, but we did go to a few sit down meals. My girls did not do well at all at the Crystal Palace, but they don't like Pooh & Co. We went there for my mom's birthday, and the girls really didn't like it. However, the LOVED Chef Mickey's, and really enjoyed the singing, waving their napkins around, etc. When we were at the Crystal Palace, my DH and I took turns taking the girls for a walk around the resturant while the other one stayed with our DS.
Does your little one look up to her big sisters? Our oldest was a HUGE help with our little ones - it was very sweet the things he would do and say to help keep them entertained.
We're going back the end of October, and looking forward to it. I'm sure you'll have a wonderful time!