PoS makes sense if these were investments. How does it help these become currencies? If it simply benefits those who hold coins, it would create artificially scarce environments where the price would go up.
Supposing you've been holding onto your PoS coins for 5 yrs, suddenly you wake up they're worth millions, you might hold on to a few but you're probably going to go on a spending spree and buy that Lamboughini you've always fancied. Pof stake will encourage spending and saving.