Gotta wonder about why they decided to put in the work to bring this house back from the dead, and do it properly, like someone restoring an ancient clock.
Control. Power. Control and power. If you do it up yourself, you're responsible for how it looks. If you do it according to Hoyle you are merely exercising the will of the architectural gods. Redo the walls in maroon silk damask because you like maroon silk damask? you monster. Redo it because some insane rich fucker liked it in 1919? You're a traditionalist. John Barendt touches on this in Midnight in the Garden of Good and Evil; Jim Williams repeatedly uses the hagiography of the antebellum south to tweak his friends and piss off his neighbors.
Of note is the fact that virtually all of the art, furniture, and tapestries are authentic 14th to 17th-century antiques collected by the couple.
Ever been to Hearst Castle? WR Hearst wandered all over Europe buying the trappings of power, crating it up and shipping it to Central California to make his architect figure out how to integrate the facade of a 14th century French church into his dining room. What you're doing is using totems of past power to touch wood and subsume it for your own purposes. Who's more impressive, the dipshit in an Aeron or the dipshit in an Edwardian chair that belonged to the ninth Earl of Spottiswoode? If you're impressed by stuff, it's gonna be the red velvet, yo.
This is why they're on the lawn brandishing guns - their entire culture, their entire ecosystem is under threat. They're being told by their culture that they didn't earn all that shit. They're being told that their wealth is not virtuous. And the underclass is right outside reminding them of their comeuppance.
They restored an organ they don't want to play for the same reason the jackass is wearing a pink Brooks Brothers button-down on a Sunday - because they're the impressive, powerful sort of people who restore organs they don't play so they can tell people how many rooms it renders useless. But the people they impress with that shit aren't walking past their house and the people will be impressed.