Intel has not produced a compelling reason to upgrade from a quad-core Sandy Bridge CPU. There should be no debate about the i7-2600k -- it is still relevant today. It doesn't crush benchmarks, but it performs more than well enough to run Planet Coaster. You don't need the latest and greatest to comfortably run PC games. Lay off the media and marketing hype. Only upgrade if there's a legitimate reason to upgrade, and don't limit yourself to Intel if you are going to upgrade.
I argue that the way you configure your system has much more impact on games like Planet Coaster than the hardware does. The number of background craplets, unnecessary services, bloatware, and simultaneous programs makes a huge impact on how the game performs. If you're letting Dropbox or One Drive sync while playing Planet Coaster, then you're doing it wrong. If you're letting Windows Defender scan while playing, then you're doing it wrong. If you're running Discord, Mumble, and Skype in the background at the same time, then you're doing it wrong. If your taskbar is filled with a dozen background apps, browsers with many open tabs, or other stuff competing for resources, then you're doing it wrong. It never ceases to amaze me how people don't realize or make excuses for all that extra junk running.
I recently had a friend complain about the performance of a new AMD 1600 not being any better than an i7-920. The reason? Dropbox, Skype, Discord, Steam, Google Update, Adobe Update, One Drive, Avast, CCleaner, Libre Office, Lexmark printer status, HP printer status, iTunes, and HP Update all running in the background randomly calling out for attention. His Task Manager startup list had 25 items enabled on it!!! Cleaning out all that crap made his computer fly the way it should. Gaming performance, likewise, improved.