If I was insanely rich, I'd be spending my money on all kinds of stupid stuff. It would probably be sports related (a Babe Ruth jersey, etc.), but I can see why people like to collect unique things. It's like having a mini-museum in your house.
Is it really so different than millionaires who collect classic cars that just sit in a garage, for instance? It's all pretty pointless, but depending on what somebody likes, hey, go for it.