I just noticed something while playing that seems like a bit of an exploit. Upgrading a constructor starship that started with two construction modules but used one of them to an identical design costs next to nothing (92 credits in my game). After upgrading it's back to two construction points so it would basically allow one to spam starbases almost for free with only the limited speed/range of early designs limiting you.
Edit: And it seems there are more things you can do with upgrading (https://forums.galciv3.com/466335/page/1/). I think the upgrade costs/time requirements need to be looked at or in my example maybe it just shouldn't give back the buildpoint.