Overall I agree with the above, however I have yet to come across a fish other than discus that have issues with 40ppm of nitrate. There's been reports of some fish being fine at 100ppm, personally I would worry at this level. I run 40ppm of nitrates out of the tap and I dose nitrates on top of that. Ideally you want low nitrates, but I don't test for nitrates.....
"No water changes in a thickly planted tank that is lightly stocked". I do advocate this method, its called the El Natural method. Also a filter is optional. Though I don't run any tanks using this method(I stock heavily) it is a viable method. I'm not entirely sure how water nutrients get replenished using this method. Aquaticplantcentral.com has a whole forum section dedicated to El Natural style of fish keeping, I'm sure that question could be answered there. I'm an hour from the twin cities and in the summer people have successfully bred fish outside in large cattle troughs(100-300Gal) no heater or filter, some do water changes others rely on the rain. I'm hoping to give this method a try this summer.