When I started spottng back in '74 (at Manch), I was informed that the xxth Jan was a common div day. Not knowing what a div day was in those days, or in fact anything about aircraft ops, I turned up at the airport expecting to see loads! Nowt!
Later though, I found its the unexpected arrivals/movements that really created an interest. Many div days at Manch come to mind. Nowadays, nearly everything is known prior to visiting an airport thanks to the internet and the hobby does not have the same interest. Besides, its cleaner and quieter - not good at all!