Finally there is the Old Testament motif of YHWH coming from Mount Zion
either to judge his people or to rescue them from their enemies - I’m
quite sure that this also plays into the overall apocalyptic narrative
in the New Testament. This is a hastily thrown together assortment of
ideas, but while I agree with the in general terms about the meaning of
parousia, I would suggest that the whole notion is a bit more complex than you suggest.

Andrew if I may point out just a couple of things in regard to your observation about Zion.  As of late I have been putting serious effort into understanding the Hebrew foundation of the New Testament (and I believe there is one).  Your observation that God comes from Zion to judge or rescue his people is crucial in this discussion.  It seems that in Hebrew, the word "salvation" is rarely used.  Rather "righteousness" is being used as a synonym to salvation.

For example, in Isaiah 51:5 we read in the typical poetic and repetitive Hebrew way:

my righteousness is near

my salvation is gone forth

In this case salvation and righteousness are one and the same thing. In Isaiah 1:26 we read that "Zion is the the city of righteousness" and in Jeremiah 23 and 33 we read that "The Lord is our righteousness."

Perhaps we should reconsider the paradigm that paints Zion and God as two separate entities.  What if Zion, Righteousness, Judgment, God, Jerusalem, New Jerusalem, the Parousia, etc are all the very same thing?  Afterall David’s strange request for the punishment of his enemies is "Don’t let them come into your righteousness" and Jesus encourages the disciples to "seek the kingdom and HIS righteousness" not ITS righteousness. 

So it seems that perhaps Christ is all those things we are all trying so hard to define: in Christ (in Zion, in New Jerusalem, in his Parousia, in his Righteousness) is salvation, be it salvation from the destruction of A.D. 70, salvation from the Lake of Fire (whatever that may be), salvaltion from societal and personal struggles, etc.