Well, I suppose there are advantages and disadvantages to concentrating cultural centers a la Japantown, Chinatown, and so on. Personally, I feel that the disadvantages tend to outweigh the advantages. To me, these zones feel like cultural quarantines that turn metropolitan areas into ethnic mosaics rather than melting pots. There's such a high density of similar businesses, it can't be very easy to set up shop in such a place. And yet, it must be even harder to run a business like that outside the enclave, because it's not where people would expect to go and find it. The existence of such a concentration of ethnic stores and restaurants seems to be a disadvantage for businesses both inside and outside the area.
I never felt that Japantown was particularly large or strong, so I'm not really surprised that it might be dwindling. The only real attraction there is Kinokuniya, where I've bought most of my learning materials. It's always just been good for a short trip, a couple hours at a time. Go to the bookstore, pick up a textbook, gawk at how much they charge for imported goods, walk around, get some food, and get back to the car before it dawns on you how small the place really is. On the downside, if it disappears altogether we'll have no ready-made destination when the quest is a new electronic dictionary or a somewhat decent Japanese meal. On the upside, we'll have a new opportunitiy to rediscover these things outside the context of the cultural zone. I think that sounds more interesting and exciting than the same old tourist trap.