We have three kids ages 7-12 and usually stay off property, but we stayed on property for our last trip. I thought we might regret having a rental car (although we didn’t have a lot of choice because we drove down, I thought it would be just sitting in a parking space eating into our budget.) but we used it a lot more than we had thought we would. We used Disney Transportation to get to Magic Kingdom one day, but during our mid day break we drove back to the TTC. This let us stay in the MK a lot later after close instead of funneling out with the huge crowd, and also let us grab a late dinner at Captain Cooks before heading back to our room. We could have taken the bus to DHS, but when I saw the line I was glad we could drive (and it also gave us the option to have my husband drop us off where I could walk with the kids to get in early and let them ride their must do rides while he parked.) We also ended up needign to go to CVS, and we got fast food (Arby’s) a couple nights too just to stick to our budget a bit. I liked having a car even when staying on property. Ideally we would never have to leave “the bubble” but I guess not having an easy way to do so made me feel trapped. I thought it was much less stressful to just get the kids in the car than it was to wait for the bus and hope they had room for all of us, and it gave us a lot of flexibility as to when to leave the park and what we did when we weren’t in the parks.
I can see merits both ways, so I think it just depends on which things you want to deal with