(srry dont have the beta yet just watching videos)
i think that when you are bombing a planet there should be enviromental consequences for example:
You nuke the north pole and now the planet is being drowned making it easyer for capture
or by consistently nukeing a planet you can create nuclear winter or green house effects that could kill the planets lifeforms and render it un colonize this could make the attacking player think about how he/she is going to capture the planet,
but if you are just looking to kill and destroy the planet than this could be to your advantage