I feel like the main plot, the founding family stuff and the characters getting through school, wouldn't mean anything without the "meaningless" subplots.
The characters all get development during these subplots, for instance the ticket book thing, we got tons of character development from that whole ordeal. How the girls deal with that situation in different ways, how it inadvertently brought MC and Hannah closer together, a major development in the Rachel situation.
As others have said, the day to day "slice of life" of this VN is what draws most people in. The plot is good too, but the characters and relationships are the important things to most people I have seen who come to the thread.