My boys are almost 9 and 12. Neither of them are big kids, especially the 12 year old, he easily passes for 9 or 10. They are both active kids, love to ride bikes, run around outside, and LOVE to swim. Our last trip was a year ago this month. The trip before was 6 months before. I didn't expect to need a stroller on either trip. On both trips, we ended up renting one a couple of the days.
WDW is way beyond what most kids typically do, even with breaks. The heat just makes it that much worse. The other problem is the crowds. This hasn't been mentioned, so pehaps I'm the only person to ever experience this. You would think that in WDW adults would be looking out for children. In far too many cases, you would be wrong. Especially at night. When people start getting ready for fireworks, it seems to be no holds barred. It's even worse after fireworks when the park starts to clear. My children have been hit, shoved, kicked, and almost knocked down by adults. This is while we try to stay out of the way of the mob. Once you're backed up against a fence or bench, you can't go anywhere. After about two nights of this, we got a stroller just to help keep them out of harms way. The stroller would still get bumped and jostled, but it was better than them having more bruises. Any yes, they did have bruises. I had more trying to keep myself between them and the crowd.
I would rather stuff my boys in a stroller and keep them safe than have them trampled by people who only seem to care about their own magic, and to heck with anybody else. I'm not saying everybody is that way, they aren't. But you know what they say about one bad apple.
Since we were going to want it at night, we started getting it earlier. The boys weren't in it too much early in the day, but it was still handy for holding our stuff. We're used to the hassle of "equipment" because my father needs a mobility
scooter, so it's no more trouble for us to have the stroller.
To the original poster, I would consider taking your stroller. You can always rent the double when you get there if you feel like you need it. You may also be able to sort of switch off. When one is riding the other can walk. Just be careful at night.
I'm sorry, but I don't buy that a normal 11 year old would get in a stroller, I really can't believe anyone actually convinces an 8 year old to get in one. 
Now, I am not opposed to strollers for older kids at Disney----it is a lot of walking. We have always brought two Maclaren Volos. This year before we left I asked DS if he wanted to bring it and He said yes, so we did. Once we were there though, he didn't use it at all. He was too busy and didn't want to be stuck in the stroller----not that he gets strapped in or anything, he just wanted to be able to go where he wanted.
I had NO idea it would turn into a thread of "I'm a better parent because..." I can't believe some of the things said on here. I really just wanted ideas and suggestions, not berating of each other. I did not expect my parenting to be questioned or the parenting choices of others. I ABSOLUTELY DO respect and appreciate both sides of the coin. Ultimately we will make the choice based on what is best for our child. I'm glad to hear so many others his age did fine. Hopefully he will too! I love the idea of walking more with him now so he'll be ready for the trip, though he is very active already, this will help him too I'm sure. SO thanks to everyone who engaged calmly and politely with respect to one another! I think we have enough to mull over for a while.
