This depends a LOT on when you are going to be at WDW. During peak times, I agree, you should get reservations anywhere you can get them. For slack times, I would say you can walk up many places and get a table. I see you're going in three months, so summertime... and I believe you would definitely need reservations. ~Ev
Before the dining plan, you really didn't need an ADR for some restaurants at slower times of the year. But with so many more people eating TS meals every day on the dining plan, I will be making an ADR for any restaurant where I know we want to eat, no matter what time of year we are going.