I did part of the effect for Rocket Days, just cause I thought it would be easy (and it was).
It's lacking blotches, hairs and scratches (the bright lines that walk are scratches in the film made by projection equipment!) but only because they require more time creating the images for them.
http://www.udec.cl/~jfuente_alba/film.cap
Nice link on L4D tech. We'll need adjustable smart-sharpening to do that one, and adjustable kernel-size blurring (samples can be fixed, kernel size just has to be adjustable).
Also, grayscale plus breaks alpha? Try adding it to the layer in that .cap and see what happens.
We need a way to apply effects to the whole screen. 3D games use a big quad that samples a buffer where everything's been stored so far. Layers cannot sample other layers in Construct. Would using Canvas work?