I think all of that is roughly about right. I suppose it depends how you define model train enthusiast. One can interpret it many different ways. A lot of people have a toy train to put under the tree, or in a box in junior's closet. Doesn't make them "enthusiasts" in my way of thinking.
But if we go with 1 in around 2100 as computed above, that would mean about 500 O-gauge enthusiasts in the Raleigh-Durham-chapel Hill area where I live (total extended-area population around here about 1 million). That strikes me as certainly in the ballpark, with a few big layouts (six figure cost at least) at the top, a lot like me in the middle, and several hundred smaller layouts or carpet setups around town.
I think the $450,000,000 figure is about right. I imagine only 1/4 or a bit less of that is O-gauge - I know 1/4 of model train enthusiasts aren't
t into O, but it costs a bit more per loco, etc., than N and HO, so . . . . I'm under the impressive the numbers work out to be about $60M for Lionel, $30-$40M for MTH, $20M for everyone else, and most. I won't go into why and where I got those numbers. I have no way of knowing if they are accurate, they are just what I think.
I think about one in five people are interested in model trains and enjoy hearing about it, and that about one in ten really don't want to hear about it and think it is silly.