I just got back from a stay at the yacht club with a 3 year old and an infant. A few thoughts:
1) the offsite stroller rental companies are great. They deliver the strollers to bell services, the city mini is very convenient in the parks, and the price is much more reasonable than the disney strollers. We used apple stroller and had a great experience.
2) the walk to Epcot and MGM is long for a kid. A 5 year old could probably do it but may not walk as fast as you would like in the morning and may ask to be carried on the way back. We avoid the boats as we find they are slow.
3) For Mk, it is a pain to bring the stroller on the bus and it needs to stay parked the whole time you are in fantasy land. Most of the time the stroller was pretty useless in Mk but it was nice to have it for the parades. Unfortunately, I found way too many people thought that it was ok to create a walkway next to my daughter when she was sitting on the curb. I just am not comfortable with people stepping over (and accidentally kicking) my daughter.
4) Depending on your strategy...Ak is a lot of walking. We go to Everest then to the safari then dinoland. This seemed to minimize wait times and allowed us to save our fast passes for later in the day at another park. Downside is that it is a lot of walking and you might need to slow down your pace if you don't have a stroller.
5) The stroller is great for carrying stuff. When my 3 year old walked we would put the backpack in her seat.
6) I feel safer when my kids are in the stroller. When my 3 year old got more than 5 feet away it could be tough to see her and I would panic.
I know many people don't like seeing the older kids in strollers....and we saw some really old kids in strollers. But 5 is still fairly young and it really depends on what your family plans to do. When my daughter is 5, I expect she will still be in a stroller.