Hey rafpug,
I'm glad my suggestions were helpful..
PT (Path Tracing) is always more accurate than HD which is a cached method.
For interior scenes though HD might be faster because there are more secondary rays going on.
Fireflies happen because of the small sundisk that is super bright, so if you make the sun invisible to reflections and refractions fireflies disappear.
There are other ways as well, like reducing glossiness but its not that convenient cause you're changing the appearance of your material.
As for the falloff maps, it's not "wrong" to have them, they just don't needed for what I believe you're trying to achieve here (transparent plastic).
"Fresnel IOR" and "IOR" give you control over falloff in a more realistic approach.
Sometimes btw when you have transparent materials its a good idea to use "Absorption" in order to control how far a ray will travel in a medium before converting to a certain color and eventually fading off.
I just uploaded another image on my previous post with a different version of the transparent plastic for the chairs.
Cheers..