In my opinion:
Fuel filters: Replace at recommended miles, not on time. Time doesn't matter, what matters is how much junk the filter holds. Unfortunately, there's no way to know without opening it up. In my experience across multiple cars, unless you feed it discount gas station gas, the filters stay very clean and can be run for multiples of the recommended miles. If you have trouble finding a filter, just keep running it.
PS fluid: It has no recommended change interval. But, 20 years is long enough. This isn't something you "must do now," but schedule it for the next time you are doing maintenance or oil change. However, check the fluid level now.
Brake and clutch fluid: The problem with these fluids is they absorb moisture over time. Therefore, they need to be replaced on time, more than on miles. Many manufacturers recommend 2-year replacement intervals. If you live in a humid environment, that's what you should use. If you live in a dry environment, 3-4 years is okay. If you track the car, at least every year. FYI, Porsche Club requires brake fluid to be changed within 6 months of track events. Another tell: If the brake fluid starts getting brown, that's due to corrosion (rust) so change it if it gets darker than amber.
With due respect to Rob's professional experience (GT@50), I dont' think the clutch fluid should be changed more often than brake fluid, as they are the same fluid and subject to the same moisture absorption. NOTE: There is a specific procedure for changing the clutch fluid, so refer to the book.