What a nice trip down memory lane! That collection looks like much of the stuff I inherited when my grandfather died years ago. I grew up playing with some of the low end stuff on the garage layout and dreamed of playing with the Big Boy when I got old enough.
Like others have said, there isn't much monetary value to what you have. A few items, such as the American Freedom Train items, might do well on ebay. Even though from a "quality" standpoint, in terms of the models' fidelity to the prototype, durability, etc. these were rather lackluster models (even for their time), a couple pieces look to be in good condition and in the original box. You might have a couple diamonds in the rough there with those American Freedom Train models.
The rest of the stuff, the Big Boy notwithstanding, was never really reliable and was mass produced enough in the 70s to avoid having any real collectability except with a few diehard Tyco and AHM fans. They're out there on ebay, and some of that stuff might do quite well. You never know what people are looking for, so I'd suggest giving it a shot.
I'll tell you right now I'm interested in purchasing at least two of the freight car models in your collection. PM me and we can discuss if you're interested.