Some people I've talked to simply don't like the fact that you can just build the ship in the middle of space... these people might buy the game otherwise.
Building - Some, or all of these:
1) only allow iron based building in space without proximity to a shipyard, using titanium requires a shipyard.
2) reduce the quality of ships made in space without the use of a shipyard
Repairing
1) replacing lost sections/parts will require the repair or shipyard.
2) allow the towing of wreckage - towed wreckage will not despawn - this will allow players to salvage ships, and repair them at a shipyard/repair facility.