You could also make expensive items require small amounts of rare/expensive elements. That way you could easily mine the majority of the elements for most items, hull plating for example would be easily fixable with basic and freely available materials. But Missiles, Lasers etc, would require Paladium, Radioactives etc that are hard to find or risky to extract.
It would stop people just sneaking off to build a super-ship for a month by mining a tucked away system if they couldn't find many rare elements for higher level equipment builds.
Mark.
Maybe, but not as much as you think. Stars are 99% of the mass of the star system, and are glowing nice and bright, showing what elements they have through the Fraenhofer lines.

If a star has gold in it, the planets will too. for that matter, scooping the star or mining the inner most world guarantees you heavyer elements.
My point is the basic makup of a star is visible across the galaxy, it needs a stat on the map 'metal rich, metal poor'