The last time I actually brought one, my DD was 6. I am so glad I had it! I was there with another friend and her 4 kids, no husbands, and both my kids got sick that trip.
I was so glad when my DD had fallen asleep in it in MGM (now DHS), so I could let her sleep and just push her back to the boat (we were at the Dolphin). She was burning up with a fever! Turned out, she had strep throat (I had East Coast Medical come to the room). I was so glad to have the stroller for that trip - I couldn't have carried her, and she was too sick to walk (it came on so suddenly).
She was 7 when we last rented one, but she tires easily.
I agree with the other poster: do what is right for your family. Although my kids hadn't used strollers at home for a while, having one at Disney was very convenient.