wow, another fascinating question. Well, from what I've heard, the "hairs" on the end of spears was thought to keep the blood from sliding down the shaft. It was, though, also thought to be confusing to the enemy. As far as the saber, the scarf that we see now has mostly an aesthetic function. In practice, i.e., practical usage, saber technique could make the scarf a distraction to the user, though it wouldn't affect his technique --for forms competition. You know, the saber wraps around the head --unlike the jian (technically). The sword tassels of today, especially the long ones. (For example, it is often said that the tassel should almost touch the ground and the tip of the sword should reach the earlobe. That's a good way to practice, I think, the taiji sword because --as you said-- it really forces your technique to be correct --otherwise the tassel ends up wrapped around your wrist. Oops. The tassel also indicates the roundness of your movements. You can actually see it. However, I don'tthink that someone would want to take that chance in a battle. Most of the people I know who just practice two-man sword sets take the tassels off. But, t the same time, the jian tassel Can be used as a weapon, much like any of the "soft" weapons --rope dart, chain whip, etc. Still, I'm not convinced that this would be intentional. More or less, the tassell follows the path of the blade, on a shorter arc, of course. When using the sword, I believe especially in Yang style, the "yi" (as "attention" is logically on the blade. Correct movement of the blade, therefore, also determines correct movement of the tassel.
Just one guy's opinion,