You should definitely check out this Planet Coaster dev diary because not only does it convey the scale of the theme parks Frontier want to build (crowds of thousands), it also shows some of the tools they're using to simulate those crowds. There are two interconnected goals - to treat every visitor as an individual and to convincingly portray large crowds moving realistically from one attraction to the next.
If you're not quite as excited about the simulation of pretend people as I am, you might be disappointed by the lack of actual coasters, thrills and spills in the video, but if you're the kind of person who follows individuals around their Skylines cities just to see how they live, this should be right up your virtual street.
I love the animations showing crowds as a sort of fluid force, sweeping through the pathways and causing blockages as they gather around popular attractions. If I can see that there are systems in place to move people around the park, and to track individuals, I'm immediately more inclined to believe that every change I make has some kind of impact. Sure, like an actual theme park, the game will live or die on the strength of the rides themselves, but it's good to see the science at the base of the whole operation.