My thanks to Nikesh Shukla for the tweet that unknowingly prompted this pleasant and super nerdly distraction from my thesis …

• The Famous Five are Julian, Dick, Anne, George and Timmy the Dog. 4 humans and 1 dog. For the purposes of this post, we’ll discount Timmy (as much as it pains me) and thus work with 4 individuals.
• With their respectively privileged circumstances, let’s say everyone has a fairly high life expectancy where they all hit seventy eight or so and thus meet approximately 80,000 people each.
• (There are other numbers around, but this is based on each of them interacting with 3 new people a day. Which is a big and ambitious number, but I imagine, something that socially thrusting and somewhat irritating Blytonian characters are more than capable of. “Here’s your paper Miss.” “DID I TELL YOU ABOUT THAT TIME ON KIRRIN ISLAND?”)
• 80,000 people x 4 gobby souls =  320,000 individuals met in total. 
• The books were published between 1942 and 1962.
• UK’s population in 1942 = 48 million (ish)
• UK’s population in 1962 = 55 million (ish)
• So let’s, roughly, say an average population of 52 million (yes, roughly, I know, shut up, this is the most maths I’ve done in years…).
• And that through their life the Famous Five meet approximately 320,000 people
• We can therefore conclude that the Famous Five are Famous for almost 1% of the population of the UK.
• So not very famous.
• Ta-dah.

(Thank you to the lovely @yayeahyeah for helping me check my maths! I am no mathematician … can you tell?!)