I am sure you can bring any car back as long as its under personal import because I spoke to them about it and I really don't know how fast it goes being in Japan as the 'freeway' that I use to go to work is 50km/h.
ivanbad, you sure i don't have to pay the 15% duty free?? cos I called them before I left and they told me those are the two items I have to pay (ie. GST and customs duty). But I hope u are rite. If u reckon I can save about 5000 that means the customs value is about 40000 for an altezza... that's not too bad.