I think that the old xingyi master that nianfong posted shows great alignment and power despite his age and he looks healthy as well. It's not very empirical but one of the ways I judge "experts" is whether or not they look healthy, no matter what their age [or whether they smoke or carry a few too many pounds].
For Bwil… I wouldn't dare try to teach using the spine and the feet to do even taiji "tricks" by using words on a computer screen. Intellectualization and old verbal analogies can only take you so far in developing specialized physical skills. On the other hand, it is fun to try stuff and one exercise that I was shown years ago that can help is also one that you can sort-of practise in public.
Find a heavy door -- preferably of heavy wood -- in a public building and stand quietly in front of it at a fairly close range, put both your palms on it at a comfortable height and relax your hands. Make sure your elbows are comfortably bent. Open the door by flexing your ankles and pressing into the ground by straightening your spine upwards [i.e., the feeling is like you are about to spring forward, up and out off of a diving board] more than by moving your arms.
As in a good taiji push/bounce, the power comes more from your feet and ankles meshing with the lengthening of the spine than it does from the arms straightening and exerting force.
At first, don't try to move the door much, just get the feeling of it moving because of your body action… later on trying doing this suddenly and with force to see if the door will open violently with minimal movement of your body and arms. P.S. You may get funny looks in a mall and be careful you don't smash the glass if it's a big glass door hitting the wall when you try the forceful version of this.
Do this ten times every day for a 1000 days, grasshopper, and soon you will be able to defeat almost any door that attacks you!