I've never ever played Korath before now, so I have no idea if this is normal, but:
When I use spore ships, I don't get a vote for declaration of war. It's just automatic. More annoyingly, after I claim a world with a spore ship, I'm not automatically taken to the planet to do set up the build queue and such, so I have to go to my Colonies screen in the civ manager and look for planets with zero population.
Also (and this may be intended, I don't know), it doesn't appear that planets captured with spore ships lose buildings that I can't build.