That’s a very nice example file, two comments though:
The reflection mapping wraps angular maps better than latlong panoramic images, looking at the reflection of the example file you posted, it seems like the same “object” was reflected twice, and judging by the angles only at a 45 degrees distance. If the reflections are very clean and easy to study, you should convert latlong panoramas to angluar maps / fisheye projections, where appropriate.
For the reflection maps, the add blend is physically more “correct” than multiply, since reflections are light photons that bounces off the surface, and therefore the light should be the diffuse color plus the reflection. Multiply, while giving a perfect mirror, makes no sense since reflection maps should not subtract any colors from the object. If the clean perfect mirror look is something one would like to strain for, it’s as simple as reducing the diffuse color to a dark color, “letting through” more reflective light.
I hope you don’t mind, but I made those two edits to your example file:
Mirrorexample-2.blend (710 KB)