At the time when in many countries Yahoo imagery was available for tracing, this was not available for Japan unfortunately. So mapping was done mainly based on GPS tracks, which turns out to be very difficult in large Japanese metropolitan areas because of bad GPS signals.

With the import of Yahoo data the initial guess was, that this is a reliable data source, but then with Bing imagery available for tracing, there were inconsistencies. So what source should you trust? Your GPS data with all the noise from high rise buildings, a former commercial data set or the aerial photos from a big company?

I think this situation was (and probably still is) very difficult to manage for Japanese mappers. GSI imagery is only partially available and not default in iD editor. Offsets of Bing imagery varies too much. Most people may see Bing imagery with or without their own GPS traces. If they don’t match, they will probably “correct” it in a way that it aligns with Bing imagery, even if that’s not correct.

In countries like Japan roads have usually no name. There are no street names as there are no street addresses.

Would it make sense to tag roads as having “no name”?

I'm living in Osaka and would be definitely interested in some Golden Week mapping in Kansai. Though I'm not sure yet I won't be in Tottori-ken during the holidays or not.
You could send a post to the OSM-Kansai mailing list (http://groups.google.com/group/osmkansai?lnk=). I'm sure there are some people interested in mapping Kobe (due to the earth quake it wasn't possible to use old aerial photos of MLIT for the basic roads as done for other areas).