It's long. I know.
Topic One : Power production
Realizing that Solar technology is actually kind of advanced when you consider it's just a few guys who landed on a planet my first suggestion would be a normal small generator. This could operate on loads of wood that are already present in the game. Or the wood could be turned into "Fire Wood" that would then be used as fuel. This is a more primitive kind of power production leaving the possibility of Solar and Geothermal being researched later.
This also opens the door for a new resource, coal. It could be mined exactly like metal but is used to power the first generator or later more effiecient specifically built coal generators. I like the idea that wood/coal would be the cheaper and more primitive way to produce power while the two current methods would be more expensive and researchable.
Finally, a nuclear reactor is almost a no brainer. Very large, very reliable, requires uranium to operate, expensive to build and research. If it blows, game over man...game over.
Topic Two : Vehicles and Fuel
I don't want to go too deep into this because others have spoken of it before. I mention it at this point because I think they should be required to use fuel. Using drillable oil that must first be discovered, then sucked out of the ground in most cases (maybe a small amount is harvestable on surface giving the player a hint to find deposits), sent thru pipelines or hauled, then refined (maybe), and then stored at a fueling station. But whatever is produced could be used to power vehicles and/or an oil based power generator. I think having many different avenues for power generation would really help the game and force players to use different strats depending on the available resources. At least for now that's how I feel because power is the most valuable resource currently despite being generated instead of collected.
I think to start, there could be a transport vehicle and a combat vehicle. The transport vehicle is for hauling and the combat vehicle has a heavy weapons platform (the vehicle is basically a mobile turret) OR an APC component designed to protect an assult group or carry wounded away. To start, make the vehicles of only a few types and maybe only make them purchasable. Once the game developes more make them customizable and give the player the ability to build and design them. 4 wheel chassis, half track, full track, and hover/flying and also different weapon options are ideas. Each with benefits/drawbacks and researchable. This could open an entire branch to a tech tree. Also, more advanced propulsion. Primitive cumbustion engines that require fuel to early game. Then Solar powered that dont need fuel but recharge and have limited wieght/space. Finally, nuclear powered that are expensive, blow up large, and are research intensive.
Topic : Gunsmithing and Combat Training.
Gunsmithing seems like an obvious improvement. Give the colonists the ability to make weapons at a table. Also, give them the ability to break down recovered weapons to their basic elements. As in, breaking down bows to wood and guns to metal. This would be researchable and skill based. HIgher gunsmithing skill is required to make more advanced weapons. And like the other topics I mentioned, primitive wood based weapons would be replaced by metal based firearms. Then later uranium based advanced lasers (Phased plasma rifle in the 40 watt range? Hey, only what you see buddy.) Also, a simliar based combat armor system. Primitive wood based armor for melee, bullet stopping metal armor, and finally some kind of awesome powered armor for late game. Finally, non leathal weapons. Designed to capture prisoners or animals alive. [Not going to invest a topic into it, but animal husbandry for food porposes should also be implemented if the better quality meals are going to require meat.]
Split the combat ability into groups. Melee, small, large. And then give bonuses based on skill level. Higher accuracy, rate of fire, or even just the ability to use certain weapons in the class. I also like the idea of making pistols more valuable by upping a pistol or small arms skill until you can dual weild them. That would make pistols (or better yet the Uzi) more relevent late game. This could also effect body armor use. More advanced armor requires higher combat skills.
Combat Training seems like a good idea too. Build a shooting range or Karate dojo and assign colonists to train. It just makes sense that a colony would have people training to be soldiers if they are under constant threat of attack by raiders.
Topic : Defense and Security
Expand the turret idea. An entire tech tree branch. Give the player options. Upgrade them so the are cheaper, require less power, are more accurate, don't blow up when destroyed, or hidden (hide underground and pop up only to be seen after they shoot). Many ways to go with this. It's going to be a big part of the game defense strats unless it's retooled to make the colonists easier to recruit and less valuable.
More combat relative structures like sandbags. Wooden spikes that slow down the enemy. Later to be replaced with metal barbed wire. Wood based tiger pits that do damage or kill. Later replaced by metal bear traps. Stone pill boxes that protect one or more colonists from melee attack and provide great cover. Also, a Pillbox and a turret hybrid that requires a colonist to operate but does not require power.
AA turrets. Designed to blast raiders landing from orbit. They try to land in your solor court yard and they get a landing pod full of flak.
Custom turrets. Build a generic platform them strap your own weapons to it. Four pistols? Two Miniguns? Two Enfields? A Minigun and two pistols? Two shotguns?
Also, we need a grenade launcher. Just like the grenade weapon but you can send them really far.
A defense network. Speakers throughout the base that blast alerts. They are wired to a Central Operations or Command desk that must be manned to operate. Later, if fog of war and LOS is implemented cameras could be plugged into the desk as well. Running turrets thru the desk is also a good idea. This would give the player the ability to set up a place for a colonist to go during an alert. So long as they are within range of a speaker broadcasting a warning they will stop what they are doing and report to a combat post. Later, the speakers could be replaced with personal radios via the tech tree. That way colonists mining on the other side of the map will hear the security alerts as well.
Topic : Research
AI. This gives certain items the ability to self operate. Items can be upgraded so they no longer require a colonist to operate or reduce the amount of time a colonist spends there. Hydroponic tables come to mind. Or the hauling vehicles I mentioned. The Command Desk I suggested no longer has to be manned. Turrents can be ugraded to function better or without a defence network.
Energy Efficency. Make things require less power.
Micro electronics. Make a new version of certain items that take up less room. Benches, food processor, turrets, powerplants, batteries.
Quality control. No more releases of power that blow up inside your base and drain your batteries. Also makes items resistant to the solar flare event.
Camoflage. Doors, Turrets, Walls, Armor, etc. Makes the object invisible to raiders/animals unless they see a colonist use it.
Pesticides. Stop animals from eating your crops.
A method to prevent the animals from all going nuts and attacking you as they do from time to time.
Topic : Story Telling
I think their should be an option to be an evil, good, or neutral colony and colonists. Each would have benefits/drawbacks. Suggestions as follows.
Good. Better trading prices. More frequent trade offers. Bodies, death, killing, etc all have more negative effects. Evil Colonists will not join.
Neutral. Can have any colonist join. Prisoners join faster. Evil acts have normal effect depending on colonist alignment.
Evil. Evil acts have no effect. Evil colonists only can join. Trade prices very high and trade is infrequent. They get happiness from torturing good alligned colonists.
Negotiate with Raiders. I think raiders should want something. Whether it's revenge, to free a prisoner, or simply that fat tank of gas. Some raiders will try to communicate demands and the player could choose to meet them. Good/Evil would play into the motivations of raiders as well. Sometimes giving into the demands of Evil Raiders wont work and they attack anyways. But a group of starving good aligned colonist might attack if you don't give them food. Or good aligned colonists might attack because you ate their friend last week.
Conclusion
I have more ideas but many of them have been mentioned before. Some of my ideas also might be repeats. I also believe that water should be implemented for fire fighting sprinklers and crop watering. The game dynamics involved would be the building blocks for my suggestion about oil since they would both be liquid resources.
Mostly, I feel that more options for power production would really open up the game. I like the idea of adapting your strategy every game to the map you are given. As it is, I always just go straight for the first thermal bung hole I see and build my base around that. Why? Because that's the best source of the most important resource, power. Taking this idea and expanding it to food production is also a good idea. More avenues to persue to feed your colonist would make the game more dynamic when it comes to choosing a strategic path.
Thanks for reading.