If the shades are actually any good at reflecting
radiated heat, then you don't WANT low-E film, you want
the light to come in, bounce off the shades, and bounce
back out, without even noticing that there was a window there.

You have a point. However, the shades aren't reflective enough that the
light would simply bounce back out the window. If that were the case, then
the shades would look like a mirror. The light tended to get converted into
heat when it hit the shade, once converted to heat, this caused the heat to
be trapped between the shade and the window, rather than just bouncing out.
Granted the window film wasn't helping matters, but the shades (Which happen
to have side tracks to seal the edges) were causing the trapped heat to
"bake the heck" out of the glass.

J.