I am going to disagree with the OP. I think planet cores should not be salvages. If only because I believe that, unless obliterated by weapon systems, planets should slowly regenerate from the core outward so that you can return to it later.
Remember in the heady days of Star Wars (A New Hope) when destroying a planet was considered a war crime? :p It's nearly a casual event in this game. (Not that destroying a StarMade planet is -that- easy.) Reminds me of Lexx.
Idea for a new NPC faction: Planetary Prosecutors. Rarely seen, but when you blow up any planet, they show up with a group of HUGE cruisers. It probably still won't be enough to defeat a planet cracker.