I've always preferred WWI planes over most others, but only recently have I really been bitten by the bug, in no small part because of WNWs. But before this, I modeled trains, cars, arctitecture, ships, etc., always from this same time period. There's just something really appealing to me, as gcn pointed out, with the wood, linen, metal, leather, etc. It's mechanical and engineered, but also has a nice hand built craftsmanship to it that later periods lack. This is also why I rarely build OOB. I prefer to scratch build parts, if not the whole, and personalize wherever possible.