excuse me if any of this is repetitive.
have a planet that you have to recolonize and rebuild all the structures/ships in its well every few minutes for whatever reason but provides some sort of bonus when you do have it colonized. maybe this could be the setup for a star that is in nova. some stars, if i remember correctly from class, explode many many times over a long period of time and that is their ultimate transference to their new type (whatever that may be)
have inhabited planets at the begninning of the game, complete, of course, with colony defense force
have a planet that moves within the gravity well, perhaps by command
have a planet that changes the music of the game when you colonize it, or comes with a special set of sounds when interacting with it
have a planet that provides unique unit/tech tree upgrades to the civilization that controls it, whether that be an individual player or everyone playing a specific race. perhaps the upgrades should go to the first player/race that controls it and no one after that. or the upgrade is such that colonizing the planet and developing it to X point (perhaps very expensively) unlocks the upgrade or the research to the upgrade permanently for the player that controls it so that the player can lose it and another player can take it over and the upgrade ability of the planet is not lost
have a planet that can only produce one kind of structure but theres a bonus somehow attached
have a planet that constantly rebels no matter how much its allegiance % is
have a planet that can never go above 10% (example) allegiance and is thus always rebelling or is easy to steal away/neutralize with culture. the secondary purpose for this planet may be that if somebody moves their home planet far away they may lose the planet and all its brilliant coolness (or something)
have a planet where ships randomly choose to become part of their rebellion force, or ships just stop working permanently/temporarily
have a planet that culture cannot penetrate and therefore spread through/from
have a planet that makes ships ssssllllllooooooowwwwwww doowwwnnn a lot
have a planet that consumes colony ships
have a planet that reflects a % of bombardment back to the attackers and regenerates its health quicker
have a planet that protects its population from going down while being bombarded and so the attackers attack the planet so they can colonize it at which point upgrades are already done, or at the very least the pop remains the same as when defeated/captured. perhaps this has an adverse effect on allegiance or productivity as soon as the initial captors are replaced. this planet may be very/expensively upgradable
have a planet that is upgradeable such that the more upgrades go into it the less well the planet does economically, etc but not at first. the player doesnt realize whats happening until its too late but you would have to NOT NAME/CHANGE the planet anything to be anything special, make it appear totally as a garden variety terran
have a planet that cannot be colonized and is always respawning a defense force
have a planet where upgrading/investment is expensive but return on investment is little
have a planet whose health/pop can be used to restore ship health/antimatter and may die when brought to 0 health/pop
have a planet that changes color or cloudiness or whatever when you upgrade it
have a planet that affects diplomacy if possible
have a planet that makes it so market ish is a better deal
have a planet that makes it so that every single ship and structure around it, friendly or not, have a boost to their defense
have a planet that assists/penalizes nearby planets somehow, like an economy boost or unlocking hidden bonuses
have a planet that requires much searching to fully explore the planet which may or may not unlock many bonuses
have a planet that can never be colonized but can be built on by anybody (not sure how that would work with the game)
have a planet that slows down/speeds up incoming and/or outgoing phase jumps by a lot
have a planet that requires much investment and time to get going but once you get it going its a juggernaut
have a planet that when you make it the home planet your homeworld bonuses get real big. perhaps the downside is that one cannot choose another home planet afterwards or that there can be no trade or refining or mining or building or uncolonizing, a true "political capitol" planet
have a planet whose gravity well is almost filled to the brim with mining asteroids, like 10-20 of em, and maybe their production is huge. perhaps the downside could be that the mining operations are expensive to buy/place and/or maybe they require a maintenance fee in credits/minerals. perhaps this can be done by adding a hefty - 0.5 or - 1 or even a -4 credits/second fee per mine (for example) or a fee to the opposing mineral
have a planet that builds things slowly/quickly
have a planet that acts as a phase stabilizer so you can go from that planet to anywhere in the system or something like that
have a planet that has a cool, big logo/symbol etched into it
have a planet that you cannot collect money from (or build pop on) but once youve colonized it you can build around it but does not require upgrades. perhaps this planet helps/hurts the structures youre building
have a planet that gives you free stuff like money, minerals, ships, structures, upgrades, tech etc when you colonize
of course when i say "planet" it could also be "star" or "asteroid" or "empty space" (like cew extractor types). if you need any help fleshing out what these planets would do and what they would be like you can email me @ uglybutz@yahoo.com and be sure to put "sins planets" or something in the subject line or i will delete it. i dont have mod skills but i do have story telling, philosophical and some astronomical and science fiction skills