ForgetsOldName wrote:
All of these have in common that they would be tremendously hard to make AND that if you could make them, you'd probably have the skills to make something similar but much more practical. Think how much more useful the Shield would be if it randomly one useful thing instead of what it actually does.
You're assuming that the Shield was designed this way intentionally. Just because someone makes a very powerful item, that doesn't mean they have full control over the process. It's possible that an inexperienced but enthusiastic enchanter tried to cram one too many effects into an enchanted shield and wound up botching all of them in the process. As a result, the shield is extremely powerful, but almost useless.
Although, this is all conjecture because we haven't seen a single magical item being
created, if I remember correctly. It's possible that there's an element of balance to the whole process: the more positive effects you imbue an object with, the more negative ones are added as well. The more skillful the enchanter is, or the more reagents he expends, the fewer negative effects are incurred. A +1 word requires a few hundred gold worth of materials to be expended, which is why they're so much more expensive than regular swords...etc.
That's all guessing, though. I don't know much about nothin'.