I haven't tried the techniques you mention, but there are a couple of things that I find make a big difference for me in walking efficiency.
One is relaxation, and the other is rhythm. And the only way I find to improve both is to walk a lot, and on varied terrain. I find that when I walk on variable terrain, as in a fairly rough trail, frequently and regularly, my feet and legs get used to the automatic adjustments they have to make to maintain a smooth stride despite the rough surface. So then I can maintain a walking rhythm without as much effort and without having to think about it at all. If I am out of practice, as it were, then there is a lot more effort and concentration required to walk the same stretch of trail. And this is regardless of fitness. So that even if I've been doing a lot of walking, but on smooth surfaces, I won't have the same facility when I get on a rough trail again.
Thus, being in shape is only part of the deal - I find I need to be in practice as well in order to walk efficiently on trails.
I also would second the breathing in rhythm idea - it does seem to help - and this ties back in, because if you can't maintain a walking rhythm, then it's tough to breath in sync with your strides.