Are you saying that if a fire burnt out your co-op / apartment in a shared building [ shared walls , shared roof, shared utility lines/ pipes] that $300,000 is not enough to replace wood stud walls + sheetrock + kitchen appliances + broken pipes + wires + paint and trim + flooring- for a 775 square foot area ?
I know NYC is expensive for material and labor but still, $300K seems like it should be plenty for 775 Sq ft.
If the brick / concrete structure of the building is compromised would you still want to live there ? Roof should be a common cost shared amongst all owners.
Your policy should have a seperate line item for your personal property [ clothes / pots and pans / furniture / electronics / etc. ]
If you want a "high end replacement" policy to cover "medium quality" finishes that are currently in the unit, i guess you could prioritize your spending that way...
Personally if the unit has a fair market value of $300K , i'd insure it for that, not twice as much. Then again if my home was completely destroyed, i probably wouldn't rebuild the same floor-plan / structure, although i have more potential replacement choices than you since it is a single family home on private yard.