Regarding RUACH: What makes us justified in believing that the import of RUACH in Psalm 146:4; Ecclesiastes 12:7 is different from the import of RUACH in Psalm 104:29-30; Ecclesiastes 3:19-22, especially when Qoheleth writes that man and beast have "one spirit" and the same eventuality? My question is a linguistic rather than a theological one. I believe that we must be as objective as possible about defining words and exegeting texts. Ecclesiastes 3:19-22 is very compelling evidence that man and beast have the same RUACH or vital force. Of course, RUACH has different meanings in other contexts.
The meaning of RUACH is going to depend on the setting of the passage we're examining. Its basic denotations are "spirit, wind or breath." In Ecclesiastes 3:19-22; 12:7 and Psalm 104:29; 146:4, I believe that it denotes "life force." My understanding of "life force" is harmonious with the view presented in Insight on the Scriptures II:1025: the word "life force" refers to that energy or vitality which is active in our body's cells.
Concerning Christian materialism: Not all Christian materialists hold the same beliefs about human uniqueness. From the perspective of science, the way our brains have developed (especially the neocortex) makes us unique in terms of rationality, language, and spirituality. At the present time, I have no good reasons for attributing my spiritual appetite or my rational and sociable nature to anything but neurobiological processes. If there is something else that explains human uniqueness, it seems to go beyond the purview of empirical and naturalistic science. But you will find divergent views of materialism/physicalism among those who consider themselves Christian. And while Witnesses don't technically label themselves as "Christian materialists," I've just found that it's a convenient way to describe what I/we believe.
Finally, it's interesting to think about the role that the human body has qua identity. The Apostle Paul painstakingly outlines a position that says the body raised is not the same corpus as the body that was sown in death (1 Corinthians 15:42-44). While his inspired comments apply to those raised to immortal life in the heavens, based on what we seem to know about the resurrection of Christ and others, those resurrected in the new earth will probably have bodies that look similar to those bodies that were sown. In other words, God will not bring the same (exact) body to life that one had in this world.