For what you're doing, you'll be happy to have a car when you need it.
I'm going to be at POP for two weeks, and wouldn't dream of renting a car. No ADRs at other resorts, and I don't plan to do anything off property.
I've heard the complaints about the buses, and for the life of me, I can't understand it. I've adored WDW bus service. It's a million notches above "public transportation," for the simple reason that you're riding the bus with a bunch of Disney fanatics just like you
But really, the only drawbacks I've experienced are ones I can live with, considering I'm saving the money of the rental and the hassle (for me) of driving to the parks, navigating traffic, parking the car, nabbing a tram/monorail/ferry (or walking) to the entrance, etc. There's something relaxing about being able to get on the bus and chat with your friends/family about what you plan to do (or what you did that day on your way back to the hotel). I love watching the children point to things out the window, study park maps as they plan their day, or giggle when they talk about seeing Mickey. And at the end of a long day, I prefer to just lean back and close my eyes, put my arm around my GF, and fall half asleep in the dim serenity.
Drawbacks to the buses? You'll occasionally wait, although I'd say that honestly, 75% of the time it's less than 10 minutes. And at the end of the day, if you follow the mob out of the park, it can get crowded on the bus and you might have to stand (which can be a nightmare at the end of a tiring day), unless you wait for another bus to come. Best fix for that is to sit on a bench inside the park, enjoying the atmosphere and music until the mobs are gone
All said and done, however, those negatives just aren't nearly enough of a reason to make me pay an extra $25/day and deal with the mentally tiring aspect of driving. I just don't relish the idea of trudging to the car, following the traffic out of the lot, finding a parking spot at the hotel... I don't want to do that at the end of the day. And having to get into a Florida-sun-baked car in the middle of the day if I need an afternoon break or I want to park hop isn't fun either.