Why the spawner tuning settings?

The way the mod manages to slow spawning and lower population caps on a curve is by deleting biters when they, as a percentage chance, shouldn't have spawned. Further, my goal with the curve is for the spawner clumps to work the way you'd expect in a conflict; most defensive resources are expended early, not linearly. So having higher population caps and faster spawning than vanilla accomplishes this, as well as managing my deleted biter situation.

Is this eating into UPS?

I haven't measured it, but it only evaluates chunks either A) where a biter was killed or B) where a killed biter was spawned from. And it only checks those based on an event, it's not polling. Finally, it doesn't set up the resource system for attack waves, because those biters aren't associated to spawners anymore.

How does Stop Exploring Planets work?

Any planet-based science pack other than Nauvis' default packs count towards the total. Space-based ones don't count. Modded planets work for this too. Essentially, we freeze evolution just below the next biter tier. Technically this should work for additional biter types and factions, though not extremely gracefully, especially if it's a lot of very similar types of biter. Adding 2-3 obviously higher or lower tiers should be fine.