HFA is a circumstantial thing in today's NFL. Certain cities, like LA, doesn't have any home field so they are extremely irrelevant but real football cities with a solid fan base create a big advantage. I believe we would have won some tough playoff games of the Smith-era if we played them at home.
I think the interesting bit from older times is the success of the wild card teams. I'm pretty sure it's a relatively small stat but they felt to be a bit more successful than some teams enjoying the bye (#2 seeds).