I'd like to offer up the observation that it seems very wasteful to have constructors be destroyed when upgrading a starbase. I mean, in addition to the constructor module, they are also a hull and have engines (at a bare minimum). These are very expensive to create, particularly the fast ones (13pc is my quickest one used in a large universe).
To give you an idea, it takes about 16-20 constructors to completely outfit (up to starbase Mark IV) a military starbase. I personally love to whip one of these out in a cluster right before attacking, but the cost is so huge.
It would really be nice if I could just come back to a planet for a retrofit and just add another constructor and not have to build from scratch each time.