Here’s a 30 second idea I had while inhaling my morning coffee. Exploration bases.
All exploration ships must leave from a special space-based facility built for their manufacture. These would work very much like a DS. Start with one in your home system. Be able to build a limited number more at a large cost relative to empire/family size. Move them to areas you wish to explore quickly to a system you own a % of planets in. If you lose a system one is in it simply heads back to your home to be re-deployed. They can’t be destroyed.
This would prevent to a large extent the problem above with instant re-explores. It would slow down exploration spread a lot so it may be viable to remove the eship build limit or increase it.
I like this, but how about something like an eship can’t be sent to a system with a planet less than fully built. You could then explore every planet in a system, but one at a time. Added to the exploration base travel time this seems fair. Gives others time to get in and build up.