Elevating the body (specifically the shoulder) does make more room for your arm to swing. Furthermore, it brings your frontal deltoids and pectoral muscles into the stroke, because consciously or unconsciously, if you bring yourself up high, you're probably not going to immobilize your shoulder joint through the stroke, and from up high the shoulder movement will push your arm faster down the stroke, as opposed to a low stance where a shoulder movement only pushes your arm down toward the table. Now the force of your elbow flex is supported by a little shoulder flex, and it adds quite a large power increase with no perceptible increase in effort.
Shoulder movement, however, is very much a double-edged sword because a stroke with more moving parts is a stroke that is harder to execute accurately. Also, if you're used to having your head low, it's hard to sight longer shots from up high.
If you want to get better power from the low position, there's something wrong with your grip, your stroke, or your cue length if your wrist feels like it needs to do tricks on the follow-through. I stay low on power shots because I don't want to sacrifice accuracy, and I concentrate on a smooth, unchecked delivery of power. It's really quite a mental trick, at least for me, to release the cue through the stroke without using any of your little muscles to "steer" the cue through the stroke, which totally robs the cue of acceleration. Once you can get the feeling of pulling the cue back and then totally releasing all tension through the forward stroke, I think you'll find that a)your wrist movements will take care of themselves and b)you've got all the power you need.
If you want to straighten out whatever your wrist is doing funny, one thing I recommend trying is to practice-stroke a while with something uncomfortable in your grip hand along with the cue, such as a cube of chalk. You won't be able to "guide" the cue because your hand won't be comfortable doing so, you'll just have to learn to let it go through. Once you're practice-stroking straight and loose with the interfering object, hit some balls that way. It'll allow you to get the feeling of not holding the stroke back by guiding it at all. You'll also have to learn to be smooth, because with the interfering object in the way, if you try to jerk the cue forward too suddenly, you'll lose your grip.
-Andrew
