Lee, I agree with what you say about body mechanics, but if someone never gets out of the ivory tower, how effective do you think they will ever be in practice -- any practice? Being able to recite the company line about power and aiki and whatsis does not equate to being able to strike effectively. I know the way that karateka learn how to punch effectively, but I doubt that anyone within aikido would ever use those methods.
Yah, of course. You gotta test it in reality, the question is just with what? Learning to hit stuff with your fists can teach you a lot if you use it as an opportunity to learn how to get your whole body into your fist, or it can just teach you how to hit with a fist disconnected from your body. Learning to kick with the whole body behind the leg is also extremely valuable and can teach you a lot about how to simply just walk with power behind your steps rather than the standard shift balance forward way.
But, on the other hand, does it have to be an arm or a leg? Wasn't O'Sensei really fond of stabbing his jo into trees and what-not? Learning to drive power down the shaft of a spear would seem like it has a lot in common with driving power into the shaft of one's forearm and one's fist (or one's leg). Certain sorts of strikes like shomen or yokomen with jo or bokken also might have a lot in relation to the action of the reciprocal sides of the body acting to generate punches or strikes (could be viewed as rotation or counter-extension, whatever flavor floats your boat). At least in the pole-shaking training I have been shown, the mechanics are extremely similar.
I would thus think weapons training could also allow one to test the effectiveness of one's coordination if you are testing against real targets/resistance and not just swatting at the air. But when it comes to weapons training, I am really ignorant about higher level aspects of it since it was absent in just about all of the aikido passed down to me or when present just the wacky-sticks variety, and what I can do is sort of brutishly reverse engineered from learning how to punch or kick effectively.