Hey, if you like Gacha games like Genshin Impact, you could suggest a "pull" system for Zenith. Zenith generates 31 crystals every 5 seconds, and players get to spend 6 crystals to pull in an asteroid from deep space into the asteroid swarm. Now, these asteroids have a 41% chance to be a common asteroid, that deals about 400 damage on impact, you know your average whatever rock. But some 31% of the time you get an uncommon asteroid, and that's a regular asteroid but also comes with 3 enhanced stardust (this is a currency that can be used to upgrade your current asteroid swarm as well as guarentee certain asteroids from the pool). 20% of the time it's a rare asteroid, which has a red color(red is cool) and this asteroid is like a mega asteroid, dealing like 1000 damage on impact with a larger AOE. 7.5% of the time you pull a UR(Ultra Rare) asteroid, which is about 50% better in all stats to the rare types of asteroids. And the grand mega pull, the SSR 0.5% chance to pull a NUR(Nuclear Ultra Rare) asteroid that does a Dinosaur-level extinction event of about half a nuke. I think this is a strong base for metal monetization to deal with the late game metal econony in the game, to give players a metal sink (ofcourse you can spend metal to generate crystals for more pulls). Players will be delighted to know that they can reclaim their asteroids in the swarm to recieve 8 crystal dust, and by combining 3 crystal dust they can create 1 more crystal, to pull another meteor from outer space.
Just a though...