Very simply take the campaing focus out of the Dungeon and off of the spoons.
Give them situations that they can not use use the spoons to solve.
They are now rich and powerfull, so give them moral and political situations that brute force can not solve. For example: a Duke has died the Duches has requested the pc's aid in escorting her son back to the castle from the school that he was at. The young boy is missing and it is discovered that the Duke was poisoned. Where is the boy? Who killed the Duke? Yes this situation can involve combat, but digging thru the castle with spoons will not help. For fun start a war. Make them choose sides, but dont make the choice easy or black and white.
Politics not your game?
Then change the enviroment completly.
Challenge them with wilderness adventures, a good trek over the mountains and into the desert is always a good change of pace. An ancient burried city has just been discovered and it prime for exploration and looting.
Challenge them with Aquatic adventures, above the water or below the water, makes no difference. Spoons make very poor lifeboats and paddles. And digging thru the ship that you are standing on is not a good Idea. Perhaps the Sahuagin were behind the Dukes death and the son's dissapearance. Heck they started the war.
Challenge them with Aerial Adventures, the cloud giants have gone to far and need to be stopped. Castle in the air made of clouds are not something I would want to dig thru. OR Perhaps they need to find a Ki-rin that knows of a weapon that can be used against the Sahuagin.
If this does not do the trick, it is time to leave the prime material plane. They stepped throuth the wrong door and vola they end up in Sigil. Sorry that was a one way portal. The only know portal key back to thier home plane is located in the Fabled City of Brass.
The trick here is let them keep there shiny spoons but change the enviroment so that the spoons are useless!