If the metaphor is not understood, the metaphor is useless. Some people, due to the lack of education, miss metaphors, and a great deal more. But this notion that the uneducated are best left in the dark, I think, is a dangerous leap towards elitism; saving decent education for the elite has been a hallmark of exploitation, and a necessary condition for the development of a society of elitism.
Nietzsche had no problem with elitism, instead, he chose to be elitism's greatest voice, and I still respect his mark of genius as a thinker. However, I think we can all agree that an interest in applying the principles of elitism to a human population, like applying the principles of strong determinism, is wholly misguided and destined to be catastrophic.
Fears of losing dignity for the uneducated reading and misunderstanding your work is nothing more than vanity. Even Nietzsche is read and misunderstood by the less fortunate, at the expense of his "dignity", or rather, popular perception. There is another old Chinese saying, Confucian, which I will inaccurately represent because I do not want to go searching the Analects for it: "It is best to be liked by good people, and hated by bad people".
Fear of losing virtue for having the uneducated reading and misunderstanding your work is just plain silly. At best, they can only tarnish the image others have of you - but why should you care? If I save a life, and somehow come out looking like a murderer, the fact that I saved a life does not change. Any virtue you have better run deeper than other people's opinion - if not, I fear you have no virtue to speak of.
Nietzsche was brilliant. But instead of keeping some people too dumb to understand him, we should educate everyone so that everyone can read him, understand him, and make the reasonable decision to reject his philosophy.
Seriously, though, the digs at 'Stache Man aside, it is a shame that some people cannot understand metaphor, that most people are completely lost when they read Nietzsche, and many others. There is no benefit to keeping them uneducated, unless by benefit you mean the proceeds from the exploitation of those with sub-par educations. Writers need to have enough confidence in their work to not worry about being misunderstood - someone will
understand, and when he does, you have your credit. Socrates is only held in higher esteem for being executed for corrupting the youth. The ignorance of post-plague Athens has not caused Socrates any loss of dignity or virtue. If anything, general opinion of the man has only grown over the centuries.
Of course, maybe no one will understand you. And that's Nietzsche's attraction in the first place. Instead of following Nietzsche, and cutting yourself off from the world, hiding away in your own mind as it drifts further and further from reality, go out into the world. Not all of us are great writer, I'm terrible. If no one understands what you write, find another profession, and write in your spare time.