Jesus does refer to Himself as the Son of God (" I and my Father are one" is one of the many times Jesus refers to God as His father, but there are specific reasons relating to prophecy and theology why Jesus refers to Himself as Son of Man. His Deity is never diminished, He was and is God. What is the stumbling block for most people is that God could become a man and humble Himself, even to dying on the cross.
If God is Almighty and He is. If everything exists under His creative word and sustaining and it does, how can any one who is mere human claim that God cannot do whatever He wishes, even when that goes against our human logic in order to bring about our salvation? (read the last chapters in Job and "brace yourself as a man" as God asks the questions of mere mortals who questioned His way of doing things to bring about the best for man and the glory of God)
Jesus as Son of Man is probably one of the most profoundest and most important doctrinces in Christianity. He who is above all powers, above all things, thought of me and was willing to come and be a human like me to ensure I would oneday be with Him in glory.
Daniel 7:13-14- I saw in the night visions, and, behold, one like the Son of man came with the clouds of heaven, and came to the Ancient of days, and they brought him near before him. And there was given him dominion, and glory, and a kingdom, that all people, nations, and languages, should serve him: his dominion is an everlasting dominion, which shall not pass away, and his kingdom that which shall not be destroyed.
This Son of Man who laid aside (but never gave up His position as God of the Universe) His Deity, took it up again and oneday every knee will bow (gratefully in worship or grudgingly in resignation to truth). and every tongue will confess that Jesus Christ is Lord to the glory of God the Father. Like Alpha, I look forward to being in the first group!