Sorry for a late reply, I've been on the AT for the past month. I hope you'll share some more about 'chi-hiking' when you've had some time to try it out.
Because I tend to do higher-mileage days, I also try to introduce variety into my strides to keep things fresh. One of my 'discoveries' last month was using a stride similar to the way racewalkers move--with lots of hip motion. I don't rely on it as my main walking motion, but it is nice to mix things up. I've used it with success on climbs, flats, and drops. I'll have to play with it more to see if there are actually any efficiency benefits for different types of terrain. I do know that it is often a welcome change, and does seem a bit less demanding on the calves.
Another method I use is taking downhills pretty quickly. I despise long, drawn-out descents, so I try to keep my momentum going as much as possible. On more level descents, I'll often go into an easy jog, just leaning and letting gravity pull me forward. I try to avoid a direct heel-strike. On steeper descents, the more extreme body motion comes into play--I try to use my arms/poles and everything below my ribcage to absorb the impact. Ankles limber, knees flexed, body low, hips swiveling. Looks goofy, but it works for me.
Also, walking backwards is kind of fun.