We were at WDW from Saturday, 10/1 through Wednesday, 10/5 on the free dining plan. I was under the impression that attendance might have been up due to the rescheduling of trips because of the high hurricane activity last year.
I found that making ADR's for popular places even several weeks before our trip was VERY difficult. And on entering the MK, there were signs indicating that there were NO reservations available at sit-down restaurants in the park. At MGM, we overheard a man asking at Mama Melrose's how long a wait it would be if he didn't have an ADR....he was told they wouldn't be able to seat him at all without an ADR.
At Epcot, in Guest Relations, they had a board that indicated dining availability for each of the sit-down restaurants for lunch and dinner. Lunch wasn't so bad, but there was typically only one or two of the less popular restaurants with availability for dinner.
If you like eating at normal times at popular restaurants, particularly in the parks, I wouldn't count on much just winging it - at least during a time when free dining was available.
I agree that the rigidity is a strong downside to the whole WDW experience these days -- whether or not you've got the dining plan, the dining plan is going to affect your ability to eat when and where you're going to eat. And the switch from taking reservations from 90 to 180 days out may have made the situation worse. It was bad enough planning out where you'd-be-when 90 days in advance so you could book your dining, but 180 days is just ridiculous. Park hours, EMH schedules, etc, etc, can all change. UGH! And so much for last-minute trips! And with Southwest only taking reservations a couple of months in advance it makes the whole experience even more strenuous.