I might be staying a night in Tokyo Station Hotel
It seems to be a conservative, high class hotel. Should I dress in business casual clothes or are normal (clean) clothes fine? I realize there is no official policy (otherwise it would be listed in the web site) but are there any unofficial rules about clothing in these kind of hotels?
Japanese hotels do not enforce dress codes: you can turn up in a wifebeater and flip-flops if you wish and they'll let you check in. Restaurants and bars in the hotels may, however, have and enforce their own dress clothes.
I went for a peek at the Station Hotel two years ago when it opened (didn't stay though, can't quite justify those prices...), and while it's indeed a luxury hotel, there were plenty of tourists dressed in standard tourist gear: loud T-shirts, shorts, fluorescent fanny packs, etc. So I wouldn't worry about it.
