Greetings,
I wear skirts the vast majority of the time, and have done Disney, in skirts. No matter the length, you do not want pencil skirts. There are too many situations where you need to spread your legs and climb. Getting in and out of Space Mountain is a great example.
I wear loose flowing skirts. In the event of cold weather, I wear those footless leggings which are so popular now and then socks. I like the combination better than tights because tights are not as comfortable on my feet for long day excursions. I like to wear a pair of thin wicking socks topped by a warm pair of socks. The wicking socks take care of any foot moisture.
In the event of rain and my shoes/socks get soaked, I do not need to change my entire lower half's clothing. I can just slip into another pair of socks.
Oh, take at least two pair of shoes, so when one of them gets wet, you have a dry pair to wear.
Denim is my least favorite fabric to wear at Disney. If you get that stuff wet, then it stays wet for hours, if not all day. Between Splash Mountain, kids spilling stuff on me, and the River Rapids Ride, and Florida cloud bursts, I usually get wet at least once. I like fabric that dries quickly.
This type of skirt works well
http://www.funkyfrum.com/product_p/e7b3-8em.htm It has plenty of volume for when your legs need to come apart.
During warm weather I wear golf skirts. These are shorter than I would wear in my every day life, but they are skort style and have built in shorts for full modesty. I usually pick mine up at the end of the summer at our local golf shop for a hefty discount. They skim the top of my knee and have a built in bike short. (No flashing problems at all). These work better than run of the mill skorts as they were built for athletic activity, wicking sweat, and being very comfortable. Some skorts are so bulky and uncomfortable, but the golf skorts are amazing.