As always you cannot beat B&G quality. Everything in the box is expertly designed and made. Have never been disappointed by their products.
If you have silver Van Richten and Legendary Strahd be ready for plenty of redundancy. Strahd had an oversized encounter card for the Count that dwarfs the oversized ones in this edition. Much of the material and maps was already in Silver Van Richtens. The big change I am still trying to wrap my head around is they give the big bads from each domain stats.
Given the nature of the domains, the personal manifestations of hell for the worst of the worst, giving stats to the Darklords opens immense possibilities. Do one of the players become the Darklord? Does a new evil take their place. Given the Darklords are bound to the domain are they off lurking ready to return? As a DM the possibilities are endless.
If you can afford it, then this alone can make the purchase worth it even if you own the Silver Van Richtens.
And then there is the addition of Cthulu...