Well, as an architectural building of stature, it rates very low, but as a place, where historic intrigues have been hatched, it rates high in Britisn history.
One may not like the occupants of Buckingham Palace or the social and privileged position that they enjoy within UK society and the former dominions.
However, that's no reason to pull-down a perfectly well kept building, that could, in the service of the nation, be put to better use.
Turn it into a museum/hotel with full public access. The Queen's and the Prince's private quarters could server as an 8 star hotel suite for visiting rich Chinese and Russian oligarchy.
It would be a money-spinner, a slab of concrete won't.
And the money made: To what use should it be put ? I would suggest: The care of wanked-out old royal race houses but, there are probably more needy and more relevant suggestions, as to what the money should be used for..