I have had one Japanese customer in the five years of doing it and to be honest, he was a surprise (nice chap to boot, very good English).
Wargaming isn't so popular over there mainly because of the time involved. The kids spend six days a week at school and most go to after school clubs in the evenings and Sundays. Likewise, the business men work long hours and so computer games are very popular, you can just switch it off whenever.
Kit making is very popular, because although it is time consuming and labour intensive, you only have to do a little bit at a time.
Model railways are very popular for the same reason (although space can be an issue when you see the size of some of the flats etc

).
I know there is a growing group of ex-pats over there (West Tokyo Wargamers being one) and GW have a foot hold, I even popped in a few years ago and we weren't accosted

The stuff I do is for wargaming and not dioramas, there is quite a difference and the people there who do period dioramas (not as many as you'd think) have the talent to do it themselves.
The Japanese appreciate and respect skill a lot more than other countries (that's how it seems to me) and although the sort of thing we do is still looked at askance there is still the appreciation there.
I hope that makes sense and if anyone has anything to add or alter (I'm going on my own personal opinion and through talking to my wife [who's Japanese and really has no clue

]) then please feel free to do so

cheers
James