can you spoil a 30-year-old movie?
Yes you can. There are plenty of 30 year old, and much older, movies I have yet to see.
Here are a few off the top of my head:
Ben Hur--wins the chariot race.
Star Trek 1--Spock doesn't die at the end
The Ten Commandments--Moses had to rewrite them himself
Godzilla--ends up reviving Japan's construction industry
E.T.--destroys Japan's video game industry
OK that's all I can think of for now.