To cite your example of your sword, you may not repair it after every swing, but after it has unequipped itself because it's condition is 0, isn't it nice to be able to use a repair hammer to get a few more swings out of it while you extricate yourself from your current situation? If your repair hammer almost never repaired it enough to get more than one swing out of it before the hammer is used up, would anyone carry a repair hammer?
The Amulet of shadows is a perfect example.. It holds enough charge, and uses enough charge each time it's used that you could conceivably go through a dozen soul gems and still not get even one use out of it. Especially if your enchant skill is extraordinarily high. I don't think anybody is actually looking for a way to make it have unlimited usage... just a way to make it work for one more use for an expenditure of a mere 7000 gold.
Where are you getting the 7000 from? Grand soul gems are 200 gold. I guess summoning Golden Saints is expensive if you can't find any in the wild and are relying on scrolls. If you only need to carry around six grand soul gems filled with Saint souls to refill your amulet, I think that's pretty reasonable. How long does it take to capture that many souls? A high level player can do it in a couple of minutes tops provided they are adept at conjuration. For such a small amount of work, you receive something like five minutes of 80pts chameleon.
I think a better "fix" would be to eliminate the Amulet of Shadows!