I wasn't talking about planet development. That falls into the "exploitation" category. Sins doesnt seem to have an issue with that IMO.
Exploration. To go out into the unknown, and discover that which you have not seen before. Sins does this to a point with the unknown planet icons. It is a die roll to discover an ice world, gas giant, nebula, or asteroid. There is still that missing element. On fixed maps you already know what is there after you played it a few times so there really is no exploration. Only on randomly generated maps does the exploration need get to be partially satisfied. There needs to be even more diversity in the worlds. More "surprises" so to speak. More risk. Like not just encountering a few scattered defenders a neutral world. More like a random chance of finding LOTS of defenders, or a chance of "oh shit! is that a hostile capitol ship i see over there?!". Perhaps discover a new random AI faction. Rewards like finding a derelict Kodiak, or command cruiser that joins your forces, or gives you that technology.
Galactic Civilizations 2 should be the example followed here. There you can discover a random minor race (friendly or not should be random as well), or find rare artifacts floating randomly in space. You can find artifacts in sins as well, but that again falls under the exploitation category after a planet is already discovered, and colonized. I am talking about finding derelict ships, Relics from long dead civilizations, and the like. Most of this would happen in the early game when you 1st start scouting out the map.
Give the feel of actual exploration instead of playing connect the dots.
ok, so I got you completely wrong. sure, some of those elements would be nice to have, what I would love is that some planets not only have militia but also limited infrastructure you need to bomb first, like 500 hp and then you colonise. also, there are mods that change the altogether static mode of planets a bit while still preserving their distinct uses.
as for pure exploration: I dont see how what you really want can be reconciled with the jump lane system. space is mighty big and there may well be tons of treasures lying around, but in all honesty it would take ages to explore it all. sure, you can add little things, like derelict ships, a map of the surroundings, a low tech if you want or a left over station, but that's not so much the exploration I think.
do you think a "search for jump lanes" function would aid that exploration part? it could be like having your ships sit there a moment and calculate where you can go from the new grav well and only then will you see the jump lanes and be able to use it. it would of course slow down the beginning quite a bit, if your cannot send your scout just along, because it might get destroyed by militia while sitting there and calculing jump lanes, but still.
or you make it a research. like stellar cartagraphy and it gives you the jump lanes to new worlds as you arrive there, but only a limited number of jumps from your hw. so at the beginning you can only explore some 2 - 3 jumps and as you research more (or possibly set up colonies closer to the limit range) it becomes farther.
ps. I think minor races were considered, but scrapped for time issues.