galactic infrastructure

upvoted.

This really has some potential! Not only in a militaristic way. Think about bonuses for economy, colonization, trading routes and population/space port management! With some diplomatic agreements, it could be possible to set up new/special inter faction bonuses, or simply share bonuses with allies on your territory.
Reading this idea also reminds me of the teleportation gates of the vaulters from ES. 

This is a fantastic suggestion! I have often felt that by mid - to -late game when the military aspect of the game starts to become more prevalent, it is far to easy to bypass strategic chokepoints on the map. All four of your suggestions would add depth to the gameplay in terms of having to choose systems very wisely when expanding early on.

I like the idea, here are some ideas of my own:

Space highway: works similar to a trade route but increases movement points along the route. diplomatic treaties to set up a highway along the galaxy.

Mining Stations: lets you get part of the bonus from a nearby special node if its outside your influence. civilian ships travel from your planet to the node and mine it. the ships can be attacked by pirates/cold war oppononents.

added some more suggestions:

-mining stations that extract strategic and luxuary resources. can be specialized in either type of resource. this would save players of colonizing bad systems just for the resources

Great Idea! Also the game could include halo-relay stations, or somthing lke that, which can reduce over-colonization dissaproval. 

Very nice! Upvoted!

I especially like the mining station idea. This would give more strategic depth to the fight for ressources.

I am thinking of intercepting resource freighters en route back to their colonies.

Additionally all types of stations should be attackable after defeating their defending fleets.

Really great!