These discussions will go on forever, and I think one reason for that is that humans have to use the Bible to try to prove their point. It seems to me, from reading every comment on this thread and many, many others over the years, that one can use the Bible to, in effect, prove (or at least establish to some degree) both concepts - Trinity and no-Trinity.
To me, therein lies the problem - the Bible may very well teach both concepts. Perhaps it either gives us contradicting indications, or it intentionally teaches both concepts. Or maybe there's some in-between - some level of existence by God that we as humans simply don't understand. After all, would God really expect mere humans to fully comprehend all aspects of His being? Could this whole thing instead be fluid - could God exist and act on both levels (Trinitarian and non-Trinitarian).
Take the Holy Sprit for example. Some say it's a person. Others say not. The Bible is used to argue both. Could it be that the Holy Spirit can act as both? Could it be a non-person which at times takes on the aspects of a person? Or vice-versa? How do we really know for sure?