I had some similar ideas a while back. A planet, once captured, is just a planet. It has it's position, making it somewhat strategically important, or resource-rich, or perhaps the location of a fabricator or other immobile valuable, but aside from that, it's just a stage for the game to take place. Without a setting, the stage really is kinda' boring. I thought of a few things, both structure-wise for the AI and environmental for planets in general. I won't go into too much detail, but a few examples....
Different AI Command stations with different planet-wide effects.
- Staging Facility - 150% Wave strength on waves sent from this planet or surrounding planets
- Minor Shipyard - Produces threat ships at a fixed m/c build rate.
- Major Shipyard - Produces threat starships at a fixed m/c build rate.
- Defense Outpost - Places turrets on the planet and adjacent planets
- Perimeter Station - Can "lock" a single wormhole in the system, preventing the player from entering or exiting that wormhole, forcing him/her to find an alternate route to the planet. (Perhaps Spire Jumpships can have immunity to this for dead-end systems)
Environmental Anomalies / Effects / Entities:
- Monolith - a massive rock in the solar system that is not passable by ships. Must go around the object to navigate to the other side, giving physical terrain to some systems.
- Unstable Wormholes: Causes slight damage to ships entering and exiting through the wormholes linking this planet to another.
- Ice Field - Sensors of ships bounce off of the ice chunks in the system, also decreasing visibility. Ships are only visible at close range.
- EM Radiation - Ships take damage proportional to their energy cost.
- Methane Clouds - Pockets of floating methane that explode on contact with a ship's engine flare. Not advisable to traverse with large fleets.
Those are just a few of the ideas I had. The pointis to give anothe rdimension to considering what systems are valuable and which aren't. Some that are hazardous can be used to your advantage if you use their position right (IE: Methane Clouds at a chokepoint, forcing the AI to traverse it before getting to your systems) Perhaps a density setting to determind how "common" the environmental anomalies and effects are, as some may find them very attractive and fun, while others may get irritated when they find their home system is an Ice field.