I have recently bought Starfarer, and i'm already playing it nonstop. Here are some of my suggestions for the game ;
I find that there is no real point in buying a high number of marines, as the option to board ships is some-what uncommon. I think that once more of the features and mechanics of Starfarer come out, that the marines should have the ability to invade planets and space stations. It would also be cool if you could fly near trade fleets and have an option to board their ships without starting combat ( That is, fleet combat. The only combat would be from the marines. )
When you invade a planet and successfully gain control of the planet, it should have some sort of effect like producing supplies, certain weapons, fuel, or money every few in game days. Planets, and some larger space stations, could also shelter extra fleets the player has. Owning atleast one planet and three fleets could allow you to own and name your own faction, which you can use to wage war on the other factions.
Space Stations could have weapon slots on them which allow for defense of a planet, other stations, or possibly even an asteroid mining area. I think that different variations of Space Stations would be helpful too, like a station that could hold ships, a merchant station that would sell supplies, fuel, weapons, minerals gained from mining, and other items between star systems so that the player wouldn't have to travel long distances to sell items, and a mobile station that can be used to render most of a planet useless through the use of a powerful plasma weapon.
Making money in Starfarer can be easy, provided you don't get screwed over and get attacked by a fleet twenty times larger than you. So, to make making money a little easier, using your ship to mine asteroids would be nice. Each mineral mined from the asteroid would take up one cargo space. There would also be different types of minerals, such as Platinum, Cobalt, Iron, etc., and would each vary in how often they would appear, and price. Alternatively, you could own a factory, oil rig, banking company, etc., to generate items that you could sell/use, or even just generate money in general. Certain one-use equipment items could be used to board unaware Trade ships, allowing you to possibly take the ship, or sabotage the ship and steal some of the loot.
These are just a few of my suggestions and ideas for Starfarer.