Stephanie,
Obviously having your own car is always going to be more convenient, as you can hop in whenever you wish.
But I have never found using the buses at Coronado Springs to be a problem. As referenced in my last answer, as long as you can use my little trick to avoid some of the transportation time around your resort, it is pretty simple and direct.
HOWEVER that is transportation to/from parks. What can be a royal pain is this: going to/from other resort hotels. What I mean by this is when you have a dining reservation at another resort, to get there you are supposed to get on a bus to Downtown Disney, then transfer to another bus to that resort. The return trip is the same again. I get that they can't have direct bus lines between each of the 20+ resorts, but those trips can be a hassle.
But of course there are simpler solutions in many instances. For instance if the destination resort in question is on the Magic Kingdom monorail line, you can just bus to the Magic Kingdom then walk/monorail to your destination. So a dinner at Chef Mickey's is no problem, as you bus like you were going to the park, then you are a leisurely 5-minute stroll to the Contemporary. But not all destinations are so easy.
BOTTOM LINE: I would only rent a car if I had someone in my party that had mobility issues, or if my trip included a lot of meals at other resorts. Otherwise I prefer the comfort of letting Disney transportation take me where I want to go.
Write me back if you want some tips on getting to/from particular resorts!
Have a magical vacation!