Hello.
Give players some purpose of conquest besides "Conqueror of Galaxy" titile.
it's a big competitive weekly, make it something bigger than just a title.
You could have made a special planet actions available. Just a couple examples:
1. special "hard to get resources", the more times of consequent possession of a planet the more rare resource a guild can get.
2. With or without those resources there could be special "projects" for developing technologies to create something special
3. You could have added some ultra hard special world boss instance. You can even open this boss's location only to those who has done the conditions 1 and 2 that I described above
4. etc etc . Just look into the future. Make the game live for years to come not only for newcomers and not only with your new storylines.
I hope It's not that hard to improve competitiveness and increase our fun.