From what little I've hear the City of Waneroo controls the beaches themselves, but the land that is used in the dunes for offroading is actually already owned by development companies and access has been continuing only until they are ready to start developing or at least get serious about the planning.
I agree that it's probably unlikely to re-open
Perth seems to have an obsession with coastal properties, wont be long before its a 4 hour drive from the north end of the city to the south!