Hi,
Jean,
You compare these artworks with low/medium items sold by Aoi-art, it is a little bit "osé" dared.
In fact, it exists a market for very high level swords and none of us (not me in all case) can afford to enter into it. Lately, was sold an Inoue Shinkai for the low price of yen 53 Millions,
I was told one of the best collection in the world is in Saoudi Arabia. This kind of person will always have enough money to afford what they want whatever the cost.
In conclusion, yes nihontô can be a good investment but only at the very high level.