Today I changed my car's registration from Nara to Kobe. I don't like the new number plates as much as the old ones - Kobe plates are a kind of status symbol in Kansai, much as Shinagawa plates are in Kanto. I have this nagging feeling that these plates might get me pulled over more often than the old Nara ones, although I can't really explain why, it's just a feeling I have (that I hope is never proved).
A few months ago I heard that Kobe plates illicitly exported from Japan were selling in LA for a pretty sum, mostly because of the Kobe Bryant case. In retrospect, I think the high price is justified; the process to get new plates in Japan is a colossal pain in the ass if you do it yourself (Most people just pay to have car shops do it for them; I did it by myself partly just to see if it was as a big a hassle as I imagined and I was not disappointed.)
I'll bet you could sell 'em your Nara plates and just tell them that they're from Kobe...it's all kanji. Nobody will know. ;-)