I'm not saying just hand stones out like candy, make them pricy, just make them a goal you can actually work towards without praying to RNG.
How would you handle the fact that there are currently ten types of stones (plus the general ones) which can turn up in bags? I can see four methods, none of which seem satisfactory.
(1) You can buy a stone after every 10 dailies (or whatever arbitrary number you like), but the type is randomly selected after you purchase it. Has roughly the same results long-term as the current system, and is still heavily RNG-driven.
(2) You can buy a stone after every 10 dailies, and pick which family it's for. This gives players far more benefit than the current system.
(3) You can buy a stone after every 100 dailies, and pick which family it's for. This would mean you would get that Undead (or Beast, or Dragonkin) stone at about the same rate as the current system. But in the meantime you get no stones, so way less overall than the current system.
(4) Ten different currencies, one for each family. Please, no.