Is learning C really a must for a programmer?

Many have this opinion. Somehow, by doing manual memory management allocation and garbage mangement one would become a better programmer.

I have little experience in C mainly because I can write terser and more readable code in Racket or Haskell. However I'm willing to give C a try just to learn these lessons that everybody keeps talking.

But I have a sneaking suspicion that I already know most of what is there to know. Can you list some useful lessons that a typical high level code dweller would be oblivious of?

The dynamic vs static debate is kinda pointless. Usually, the use cases where dynamic allocation makes sense usually won't make sense to use static allocation and vice versa. For the two extremes: Media editing applications have to expect handling arbitrary amounts of information but the application can be installed on arbitrarily specced hardware to handle the job. Traditional critical control systems handle fixed sized arrays of numbers with filters, transforms and heuristics applied over it, strings shouldn't even come into the equation here except for a string table, and the software is tailored to specific hardware.