I had my DGD who was a tween at the time. The rest of the family was going to take a tour, so the two of us had a quick snack for breakfast, and we headed into the MK alone. It was so nice! Just the two of us, we wandered aound NFL, which was just in the process of opening, went on a few attactions together, had lunch at BOG, and toyed some more. The only thing I wish we had added was tea at the Grand, which I would totally do. Wehad one planned, but canceled and to this day I regret that we did nto keep the time we scheduled, she was studying "tea" in her cooking class at school, and I think that she woudl have enjoyed it.
Now if your teen is older I would definitely plan a resort day, including soem shopping, a nice tea at the Grand or a DS day where you can meander though the new shops and stop for lunch.