What about a meal with the Tremaines and a few hours at the Grand Floridian? It's very beautiful and grown up and probably completely unexpected.
Or a hot air balloon ride over DTD. I know it is under construction but it is still so much fun to walk around at night, have desert and drinks, listen to music, try on hats.
I personally don't think you need to add any magic to the parks, eapeciay for a first timer - they are enough by themselves.
Plus I agree that hearing about it and being there are very different. And ANY best friend trip is super special in my opinion. I wish my bestie and I could get it together to plan one anywhere! Between kids and jobs and husbands we've been trying for years....
HAVE FUN!!!!!