A good memory is undoubtably useful, even in the modern world.
Mnemonic techniques can be interesting, regardless of whether they are useful.
Mnemonic techniques can be useful for niche tasks like memorizing playing cards, although that is not helpful in daily life.
Some people who discover the power of memory palaces etc. think for a while that they’ve found the solution to everything related to memory, but I find that there are more important factors: attention, assimilating new knowledge into existing knowledge, understanding the meaning behind data, knowing what’s worth memorizing and what is better to research on demand, flashcard training, … these are often more effective.
I asked a similar question a few months ago—“Have you used Memory Techniques in an Interesting Real-Life Situation?” and got some interesting/surprising responses from people who are experienced in mnemonics (including Anthony Metivier, who teaches mnemonics), that might provide some answers to your question.
So in summary: I’d say mnemonics are useful for competitive events and for some life situations, but for everything.