[2020] Are challenges worth completing???

Is it the fastest way to gain XP? No. Is it fun to go out and kill some zombies? Sure! They're like the buried supplies quests. If I have a vehicle, I can drive over, bang it out, and be back to the trader in an hour or two of game time.

I mean, people run extra forges for the express purpose of getting screamer hordes, because they want more zombies to kill. That's a bit counter-intuitive for a survival game. But if the setup to kill some zombies can be re-framed as, let's proactively clear out a flareup of zombies before they become a greater threat, or let's get on a faction's good side by taking caring of some zombies for them, that seems like a better framework to me.