This seasons Standard decks probably arent the best indicators of required counts as the mana is so absurdly good, but looking back in time, you probably want 9-11 sources for a splash of a couple key effects and fifteen+ for a solid commitment
Cards such as the Snap Magikarp Card and Blastoise #2 First Editions from the Base Set are particularly sought after and can be worth a considerable amount, especially in pristine condition
The main reason the hand-smoothing doesnt change up the format is because of land variety
Another strategy that mono-white loves to employ is life gain, and Voice of the Blessed is all about life gain
Double strike with prowess is something not every creature can survive, and you should always have combat tricks and spells that give some form of evasion at hand to make this a serious finisher card
I definitely expected to see more decks to explain this kind of spike, though perhaps the Doctor Who cards sold worse (and are now rarer) than I realized
