The only time I ever wore heels inside a Disney park was October 25th 2008. They were on my feet for a total of 20 minutes LOL. Here is the story
My parents and I were getting ready for the Party for the Senses. I had picked out a very cute outfit, black capris and a silky purple tank top. I was trying to decide between wearing black suede flip flops that I know are SO comfy or black leather heeled sandals. Well DMom chimes in that the heels will look nicer so I caved and wore them.
We took a taxi from CSR to the BC. Here is where the walk of He-double hockey sticks begins. We walked through the BC to the end by the quiet pool and wandered out the path closest to the International Gateway. Did I mention it was about 100 degrees out? And we were getting to the International Showplace (where PFTS is hosted) very early to get our spot for the "Running of the Bulls"? By the time we arrived at the Gateway my feet were sore, but bearable, a bit of rubbing at the heels and pinching at the toes.
We then wandered from the Gateway to the Showplace, a relatively short walk, but by the time we arrived at the PFTS podium my feet were killing me. We staked out our spot right beside the doors (1 hour early i might add) and i felt something dripping from my leg. Yup...it was blood

From the backs of both my heels were trails of blood from the places the skin had been torn off. Now these were not new shoes, I had walked all around downtown Toronto in them with no issue. It was the rough terrain (that textured pavement is a witch) and the intense heat and humidity!
So, DMom, feeling horribly guilty that she had talked me into wearing the heels went off to find me better footwear. The only thing she could find at the International Gateway? Black & Red sparkly High School Musical 3 flip flops

I was not amused, but it turns out they were incredibly comfortable and you couldn't tell that they were HSM once they were on my feet. Though my black suede ones, sitting back in the room at CSR, would have been the best option
Lesson: Even if you are used to heels, the conditions at Disney parks make them unbearable! Even in the late fall!