There are three levels of "divinity" (for lack of a better term). The highest is "Word of God," ie, the literal word of God, as spoken to a prophet. This includes the Torah (Pentateuch) and Prophets. The second level is "divinely inspired," known as ruach hakodesh, in which God, in his mysterious ways, 'inspired' or had a hand in the composition of the book. This applies to Writings. The third level includes secular works, which do not have any divine inspiration.
Books written by great rabbis on Torah subjects are generally accepted to be on the second level, "divinely inspired." This is because they become part of the Oral Law, the grand tradition that interprets and explains the Word of God. It is accepted that any work which interprets the Word of God itself has some divinity, and is thus "divinely inspired." Of course, depending on who you ask and the perceived stature of the rabbi in question, a work could be considered to have more or less divine inspiration.
Maimonides wrote many books. Those which are secular in nature, such as his works on medicine, are considered not to have been composed with divine inspiration. Those works, such as the Mishne Torah, which deal with Jewish law and tradition, are considered to have an element of divine inspiration.
There are opinions which hold that everything is divinely inspired - every action, every object, etc, but these are a minority.
There are differing opinions as to whether the writings and sayings of truly great rabbis, such as those in the Talmud, on secular subjects are also divinely inspired. For example, please see Rabbinic speculations on history .
Many Progressive Jews believe that the Torah and Prophets are not necessarily the literal Word of God, but are merely divinely inspired.
Finally, Maimonides, and his works, were quite controversial when they first came out. Those who disagreed with him would have obviously assumed that they were not divinely inspired. Since then, we've accepted his works as part of our tradition.
(Divine inspiration is also considered to be at play in the determination of which works become part of the tradition.)