Antisocial's points are very good. It's a shame that type and temperament theory often get lumped into the same category as astrology, when one deals with the part of our persoanlity hard wired into our brain; and the other deals with remote objects configured into imaginary characters.
Another point, that was in the news a few years ago, but missed and forgotten, is that there is really thirteenth sign!
They had determined that the constellation Ophiuchus actually lies on the ecliptic! Perhaps it didn't anciently; but the stars are in fact moving. That one falls inbetween two others in the late winter; IIRC; Aquarius and the next one; throwing off people who are near the edges of one sign; into the next.
I'm not a hardcore believer in astrology or anything, just wanted to suggest some things because it's interesting to think about.
For point 1 -- If we lived on Mars we'd probably have to construct a new astrological system based on the placement of constellations relative to Mars (would make for an interesting scifi novel, ha). If someone just lands on Mars, his/her astrological makeup would remain the same but the effects of the stars/planets on him/her would be different. I guess that could be applied to points 2 and 3.
I don't really understand point 4.
I was thinking about things you have said but that would actually destroy the entire thing.
As for the part 4.
From simplystic perspective.
All planets are moving around the sun and in one plane and if you watch from some planet or sun behind the planets there are constellation.
But if you are moving vertically from that plane all planets will fall out from
12 astrological constellations.