The winners are the parents who have happy kids at the end of the night, although you wouldn't know it from some of the posters on the DIS! It's like a badge of honor or something...."my kids would be MORTIFIED if I mentioned a stroller after the age of 3!! I win!!"
We rented one for my DS when he was 5 year old, who gets random, severe leg cramps (thankfully seeming to be outgrowing them now that he is 8) but when one strikes he cannot walk. Luckily we never needed it for that reason, but as our first time as a family in WDW, I rather enjoyed using it in each land for all of the junk we brought. Haven't made that mistake again!!! LOL
I thought that we would really need it at park close (we were there from 9am until after Wishes), but I ended up returning it empty while DH and the kids staked out our spot for Wishes. DS was totally fine. We did not feel it was needed for the next trip when he was 7. However, IF we felt it was, I wouldn't let anyone else talk me into not getting one just because their superhuman child can walk from here to the ends of the earth.
Do what you need to do to keep everyone happy!