The Walstead method is pretty much along these same lines negating the need for water changes or filtration. Take a look at it and see if that help you make sense of what we are saying.
Plants dont release ammonia. The BB turns ammonia into nitrites and nitrates, which are used by plants as food. Plants dont take ammonia directly from the water like the bacteria does. The only difference you would see in a heavily planted tank vs not planted is the amount of nitrates (which tell you how often to change your water). In an understocked heavily planted tank, you can get away with not doing water changes for a very long time, since the bacteria takes the toxic ammonia and turns it into toxic nitrates, then the plants take the toxic nitrates out of the water and convert it into growth of the plants. When we do maintenance water changes, it is generally to take the nitrates and ugly solid waste out of the tank so it doesnt promote algae growth and poison the fish. Plants do some of this for us. They generally dont excrete anything but carbon dioxide in the process. Perhaps if you had rotting plant debris in the tank that might add something, but thats another story and you didnt mention your plants dying. If you have ammonia in your tanks that isnt being converted, you lost your bacteria somehow and your tank is no longer cycled. Maybe you had some chemical accidentally get in on your hands or a cloth or something, but I would think that the fish would show signs of that first.