Planetary engines would be great. I'll put them on every planet. If a star is about to explode, I'll warp all my planets out of the system. I might move ALL of my planets to one system and protect that one system with everything I've got.
Once I've researched sphere worlds, I'll put engines on those and gather them all up in one spot. All the ship training facilities will stack and the ships built there will instantly be at 20% experience.
Edit: move all the planets to the same spot, too and form a fleet.
Attack using a fleet of sphere worlds filled completely with weapon platforms!
