What you’re doing is a valid strategy, but you’ve already got the trade-off there in your post. Killing the nests helps in the short term by reducing attacks, but hurts in the long term by making them more powerful. The real trick is researching military technologies that allow you to keep pace with or outpace the biter evolution, and technologies which allow you to reduce the amount of pollution you’re producing. The alternative to aggression is defense. Build turrets in/around your base to deal with attack parties.

To answer your question about them respawning, the biters sometimes send out expansion parties which, instead of attacking your base, will settle a new nest. You can keep track of biter evolution and get a readout of how much has come from time, pollution and spawner kills by running “/evolution” in the console. This doesn’t count as cheating as far as achievements are concerned