My guess is most of our deeply felt cultural nostalgia for a bygone age of perceived quality of and in a medium is nothing but a historical lack of real options due to limited competition and resources, which the then young audience, now aged, naively convince themselves of the laughable and pitiful notion that what they were then consuming was the apogee of the medium.
This partly sneering reaction occurs in me every time I hear an aged critic wax eloquent about a movie or a book from a that bygone age of thin completion and even thinner real options and stamp their product as the pinnacle of the medium, invariable lamenting that it has been a downward spiral ever since into the current swamp.
A typical TEN BEST EVER list (of books, cinema) from anyone aged over 40 will prove this above hypothesis quite effortlessly.
http://content.time.com/time/arts/article/0,8599,1578073,00.html
http://www.rogerebert.com/rogers-journal/ten-greatest-films-of-all-time
Third Eye Observations 
Possibly just a month ago and I would have agreed wholeheartedly… the original Italian Job makes me wince at the poor quality of acting. However we recently watched the 1947 version of Miracle on 34th Street and it was an absolute pleasure. The acting was suberb, the quality of image definition was remarkable too. I’d hazard to say it fits easily into my list of movies I’d watch again & again without issue.
I also think that the literary side is hard to quantify… the volume of literature from bygone days was vast. There certainly are classics out there in abundance… how many of today’s will make the same category? Probably not as many as we think. Lord of the Rings (hardly a new book set anyway) aside, I can’t think of many fictional books I’ve enjoyed so much I’d pick them up again before starting a new book… Game of Thrones maybe (but that’s more to do with the awkward mid flow hiatus we have right now than anything!). Of course, the other way to look at the sheer volume of available literature right now, is that if you throw enough dung, some of it sticks… I don’t believe we’re living in a literary era of amazeness.