The Walstad method is, at heart, very simple. Most of her book gives the technical background, but you don't have to understand it. For me, it's all summed up by her as "Essential to my natural aquarium is moderate lighting, a substrate enriched with ordinary soil, and well-adapted plants." That's the nub of it. The biggest difference from most is the use of ordinary soil as a layer under the gravel, rather than one of those ridiculously over-priced "special" substrates.
As far as water changes are concerned, I see no reason to change water so long as the parameters are OK. I wouldn't go as far as Walstad ("I change about 25 to 50% of the water every 3-6 months.") but neither do I see the need for a ritualistic weekly water change without good reason. The Walstad method is really the idea of the balanced aquarium revised and updated. Large water changes are a good way to "unbalance" a balanced tank. The main reason for water changes appears to be to reduce nitrates, but strongly growing plants will themselves use up a large part of the nitrate load.In many tropical areas, rain falls for only a short part of the year. I've lived in a part of Africa where the dry season is 9 months long. The rivers rapidly dry up into a series of pools which then shrink in the heat (40oC every day). Fish are trapped in these pools in conditions which would seem intolerable, but they survive and many breed at this time. When the rains come, they are suddenly exposed to a torrent of water 15o cooler, but they live through all this with no problem. In the Amazon region, and I'm sure in many other areas, fish collectors can only catch many fish when they are trapped in pools in the dry season, as they are much too dispersed when the rivers are full. Apparently millions of Cardinal tetras can be found in some of these pools, where they will stay for months. Obviously they don't get any water changes during this period.