I agree with your last sentence but there usually is a reason a classic is a classic. Same applies to literature.
However if there is one thing I have learned is that everyone has different tastes. My wife cannot watch any film made before she was born while my golden age of film is about 1940 to 1970. I will take All About Eve, Double Indemnity, the Thin Man, and anything with Humphrey Bogart over anything released these days. That is not even getting into classic foreign films.
A key component of classic films is that they weren't able to distract special effects, or even colors for some, so plot was that much more important. I can't imagine that mumblecore will survive the test of time but I could be wrong.