I'd like to se Starship production separated from planetary production. I think it was in a StarWars game I played eons ago, planets could only produce small space crafts, like sensor drones, star fighters etc. (in that game it was X-Wings, Y-Wings, Tie-Fighters etc.)
Each planet should be able to have a number of orbital ship-building facilities for building larger ships; these could either be shipped in or built on planet. Furthermore SBs should also be able to build ships. This would not create unlimited ship production, since each facility would require money, raw material, and possibly crew in order to operate. Whether raw material comes from planet-side or space-based mining doesn’t matter. This will also help alleviate the problem of having your ship-building and repair facilities located far from where you need it. Of cause you'd have to protect the supply-lines to the bases not in territory controlled by you or they might run out of raw material.
To get an idea of what I propose look at the way it's done in SpaceEmpires, each planet of a certain size has a free space yard, all other space yards are build on ships and star bases, either in orbit or deep space. Since building ships requires resources ship building capacity is not the only limiting factor for ship building.