well i'm a big fan of b movies and b movie posters. I have hundreds of them! so i like the concept.

If you are going to do a filter in PS it should be a painting kinda one. most of these old posters are really well painted in a style that is hard to recreate.
if you are going for a title shot in a fake movie just desaturate it, as it would probably be b/w. you could think about trying to create a technicolor effect in photoshop. i'm sure you could find a tutorial for it.