Train Layout. Good...or bad idea?

Sooo...recently Brenden and I have been going back in forth about his train layout that he wants in the basement of our house in the future. I think it's completely pointless because it costs so much money, time, and it takes up a lot of space. But he insists on having one, because "they're awesome". But that just doesn't seem like a good enough reason to me. And I really have no idea what these things are really like, so I decided to look up some videos of them on youtube, and this is one of the first ones that came up. It's so much more intense than what I imagined. There's so many tiny houses and people and animals. And there's so much detail, I just can't imagine him putting all this together! The guy in the video said that he spends at least 40 hours a week in his basement. That's like having a full time job! And Brenden already has one of those, so I don't see how he's going to manage both. But he insists on having it one way or another. And another reason I don't think it's reasonable is because two of the guys he works with have layouts in their houses, and they've spent thousands of dollars on the engines, cars, and building it! I don't know where he thinks he's gonna get all the money to do this. But...I'm trying to be reasonable instead of shooting down his dream, so I'm starting to look at the more positive side of the situation. It will be a great thing for our kids to look at and play with when they're at a reasonable age, it'll make him happy...ummm...okay so there aren't that many positives to it. But it'll make him happy. And that is what I want. But I'm still not fully convinced.