Q: Do you believe in a literal “Jerusalem ABOVE” (Paul, Galations 4) still? If so, WHY? If not, WHY?
A: Rev 21:1-27 does indicate a Jerusalem/Tsiyon will come down from above after the old heaven and old earth have passed away. I can only assume the new Jerusalem will come down upon the physical/literal former Jerusalem/Tsiyon. There is no physical Temple in it, so... again... I can only assume that the people/assembly of YHVH will be living-stones (figuratively) patterned after the former Temple. Whether or not Ezekiel's Temple will still be present below it, I'm not sure. Will the former Jerusalem and Temple survive the cataclysm on the Earth? I simply do not know. Scripture doesn't seem to say specifically, from what I can recall.
Regarding Galatians 4:24, the author is clearly speaking allegorically about two covenant women. The author actually says he is speaking allegorically. He doesn't say the new Jerusalem itself is allegory. I think that is important to note. Much of Revelation is interpreted to be allegory and indeed some of it is, but the allegories are generally alluding to actual physical/literal future realities, in my view.