Re: Why the 1970's?
It was wise for Singer & Co. to not have the film set in the 1960s: Vaughan and his team acquired a lot of mileage out of the period (with the Bond aesthetic & such,) that it is nice to see a period that is not used frequently in this genre and has a lot of cinematic potential. Personally speaking, the Bronze Age is my favorite era of comics, and the 70's marked the release of a lot of good films (Alien, Star Wars, The Black Hole, Soylent Green, and so on.) Plus, it will be sonically and visually pleasing to have the culture of the decade refracted through the script.
Life is one vile task after another.