1. There is a contrast between grubby, stinky but surviving Edain, and clean, pretty but dying Eldar. Whatever does it mean?
It is interesting to note that in this version, the elves chose to stay and help. For some reason or other it mattered to them to see the world they loved inherited by men rather than orcs and to see an age of men come rather than an age of darkness. Elves really love the world in an amazing and profound way, it seems. I guess this is part of what makes them beautiful below the surface. It makes one wonder what the nature of the connection they feel to it is precisely ... although that information may be critically important it appears to be missing.

2. The main hero death in FOTR was Boromir, in ROTK it was Theoden. How does Haldir’s death fit in with those two thematically? Or does it?
I think that if Haldir had asked for a pardon for interfering in the lives of men or for some other realization of personal failure in some way, it would fit more - as it is I don't think it quite fits the same way.

3. How does this Aragorn/Haldir death scene compare with the Aragorn/Frodo death scene in Moria?
In Frodo's case there were secrets that became revealed while simultaneously saving them all.

4. Other thoughts?
Not at the moment, no.