Welcome to the land of posting. Yes, we usually discuss D23 things in the other "land", so we'll see if this gets moved there by the mods.
We went to the first D23 Expo 2 years ago, really enjoyed it and are going again! Our experience was the total opposite of the previous poster's. We went each day and had several times where we wanted to do more than one thing that was scheduled at the same time, so we had to choose which ones we wanted to go to more and do those.
The panels and other presentations were great, seeing Johnny Depp, John Travolta, Nick Cage and the others (Miley Cyrus, not so much!) were all total surprises to us, since we had no idea going into it what to expect. This time, we also have no idea what to expect exactly, so we're both looking forward to being surprised again, by whatever they present to us.
Last time, we stayed at the DLH and the Candy Cane Inn, since rooms were scarce, so we had to split our time between the 2 places, to have a room for the whole time we needed them. This time, we're staying the whole time at the Hilton, next door to the Convention Center, since last time there was way too much time and money wasted, driving to and from the CC and paying their ridiculous parking fees!! If you stay at the Hilton, they have a special D23 Expo rate, so be sure to ask for it, to see if they still have rooms available at that rate.
Do you already have your D23 Expo ticket? If so, you'll be getting, or they'll be posting, a schedule of events for each day of the Expo before the Expo starts, so that would be the best judge of how long you should stay for, depending on what you want to see and do.
Here's a link to the accommodations and other info on the Expo page: http://d23.disney.go.com/expo/book-a-trip.html
Hope you have a great time!!