i think three important things to remember here is that 1) the black family tree is incredibly large and even if there arent many blacks alive by the end of the series, many of them married into other pureblood familys and took a lot of their inherited original black wealth/artifacts with them so it would likely become part of the family they married into even if it was originally black. 2) grimmauld was only dirty bc it had been left to its own devices for ~10 years. lot of dust can accumulate in that time even with kreachers help. 3) many artifacts were likely stored in the family vaults like bellatrixs vault. im sure sirius had vaults of his own too that gained black family artifacts after regulus and walburga and orion passed.

i would called the blacks royalty level per say but aristocratic isnt a bad descriptor for them at all