The Kirgles are demanding tribute. I should do some of their missions, it'll shut them up... At some point I need to plant this colony. Is spice being wasted by lacking storage? And who will buy my stuff...
Spore. By the time you get to space age, it's very realistic. There's always something to do: once you've finished everything else, you need to collect spice from your colonies/planets. By the time you've done that, there'll be something else to do, guaranteed. That's why I prefer the creature stage...