Having two identical bikes, and I mean "identical" as in "clones", and one having the japanese labels, km/h gauges etc, I would probably pay 1 or 2 hundred more bucks for the sake of "weirdness", but not more.
Now, if the japanese bike was only sold there, it would be scarce in itself and it would command a higher price.
German CB750 had different blinkers and a couple of different things. I don't think anybody in the UK would be willing to pay extra for a german bike just because of it. Obviously, it is easier to put a german CB750 into UK than a japanese CB750 into US, and for that reason, finding a japanese bike in US is easier than a german in UK, but that alone doesn't seem to me such an argument to justify a "collector's price".
The "japanese edition" would be, in my opinion, "the icing on the cake" if the bike is in good shape. It would help to get a few hundreds more or to make it rise above the competition in the selling market. But who knows, somebody could be dying to buy the bike he imported from Japan and have a checkbook and trembling hand ready....