Several times ran across a system with 3 or more potential colony worlds and several 'dead worlds' that are quite distant from any core world. This is a great chance to upgrade one or more 'dead' worlds into a size 5 planet, colonize the colony candidates and make the class 5 a core world with tile upgrading enhancements. Adding a shipyard and an economy star base could make this a worthwhile system.
Alas, currently no small size worlds can be made a core world.
Any chance this could change?
luceo non uro