Why cant we upgrade the building where mystic vision is and get better rewards the more it’s levelled up ??
Good idea， but…
They won’t waste time on buildings which you need not spend
Well, one could argue that SG/Zynga does make a small profit from the mystic visions. Might only be $0.01 per click (or perhaps even less), but those pennies can add up when you have 1.5 million daily players. There are many f2p games that survive on advertising revenue alone.