We just got back. We forgot our stroller but had a condo that came with one and so used the very cheap umbrella stroller there for the middle days of our trip. But had no stroller the first and last days. Our daughter is an extremely active 5 1/2. Really ponder what "slow down" means to you and your family. Our daughter never complained, she loves to walk. But we missed the stroller on those 2 days. Here's why & when:
When going back to your car or bus in the afternoon for that nice break (that all the above parents recommend) you walk across the blazing hot pavement at a tired 5-6 year old pace. It's hot and not fun for the parents.
At rope drop when you are trying to get to that first ride all the other people are cruising to their first ride. You are letting them all pass you while you walk at an awed 5-6 year olds pace.
When you stop and try to figure out where you are going next, someone can't give the conversation their undivided attention because they need to keep an eye on the little one. Or else the little one gets lost. We are very organized and these conversations are limited but just the same one day it was raining and we were trying to change our plans and get ponchos on people and, of course, a little one got lost.
We often park the stroller in an area (like the middle of Tomorrowland or Fantasyland) and leave it there for hours at a time. But just the same, for entering and leaving the park and for transitioning to another part of our day, we like a stroller for our children under 7.
My dh who hates strollers said at the end of this trip that not having it for 2 days did make those 2 days worst as he was more tired. The first night we stayed until Wishes and that tiny little girl who seems so light, rode his shoulders out to our rental car. He said she was NOT so light as he thought. Comparing that to our Fantasmic exit where he quickly pushed her out with no worries of losing her he agreed that if our next trip was within the next year, he'd still want a stroller.
Personally, I like to walk at my pace. Not the pace of a child. And I never, ever, EVER want to carry a child over 3 any long distance in the heat and humidity of Florida.
In the past we have taken trips to our local zoo before a WDW trip or on a long hike to get a real feel for it. Walk a mile or two away from the car. In the heat. On day it's about to rain. And see how the kids/parents do at walking a pace everyone is happy with when it's 100 and pouring.
I would feel goofy with my daughter in a stroller in my regular life. But at WDW, for us, it makes our trip better.