Yes, I know which passages you are referring to. Here's a quick rule of thumb for you: when Schopenhauer and Nietzsche differ on some point, Nietzsche's view is the correct one.
In any case, there
are a couple of mistakes in these essays, and the greatest one just so happens to turn around the use of the concept "will". So I'll make a little effort to explain it here.
Schopenhauer says:
Reading and learning are things that anyone can do of his own free will; but not so thinking. Thinking must be kindled, like a fire by a draught; it must be sustained by some interest in the matter in hand. This interest may be of purely objective kind, or merely subjective. The latter comes into play only in things that concern us personally. Objective interest is confined to heads that think by nature; to whom thinking is as natural as breathing; and they are very rare.
http://insomnia.ac/essays/on_thinking_for_oneself/This is, strictly speaking, wrong, because "objective interest" is a
contradictio in adjecto. Interest is always subjective -- no one can be interested in something "objectively".
Still, we can see what he means by this, and what he means is to a certain extent correct. The geniune "thinker" does indeed at first glance seem to have a second, "objective" intellect, which looks at problems from a detached persepective, and is willing to follow them wherever they may lead, even if that means endangering his own security and well-being. But that is only the "first glance" conclusion. If you look deeper you will always find an ulterior motive. Just because someone might risk himself for something doesn't mean that he has no reasons for doing so. Quite the opposite in fact! The more you are willing to risk the more must be at stake for you! -- This is a universal law.
Here's another passage involving the will:
No difference of rank, position, or birth, is so great as the gulf that separates the countless millions who use their head only in the service of their belly, in other words, look upon it as an instrument of the will, and those very few and rare persons who have the courage to say: No! it is too good for that; my head shall be active only in its own service;
http://insomnia.ac/essays/on_genius/
Again, we understand what he is saying, and it is correct up to a point, but only up to a point. Because the truth is that even the "genius" uses his intellect as an instrument of the "belly" -- he cannot do otherwise -- only the belly of the genius is so much larger in size than anyone else's, it requires so much more to sate its appetite, that he is willing to take greater risks than anyone else in order to achieve this. And the quest for insight, that noble quest which Schopenhauer idealizes (and therefore falsifies), is simply the ultimate thing one can pursue. -- It can also ultimately prove to be the most useful and the most profitable. -- Schopenhauer is just being hypocritical at this point. He is perhaps the least hypocritical of all philosophers, though, so we should excuse him for this slip up.
There is a lot more to be said on this subject, but this should do for now.