Part of buying used car, to me, is trying to get an accurate idea of the cars history... if the owner of the white car doesnt know its got false KMs then its pritty poor on his behalf (aftermarket speedo automatically = false KMs). What false KMs actually means to the individual buyer will change but it is something you should at least note in your pro/con's of the car.
with regards to the N1, the more you drive it the greater chance things might break and if you blow a turbo or spin the bottom end (drop a valve, do a head gasket, anything that requires major parts to change, perhaps including a 100,000km service) in it you can kiss the whole investment thing goodbye. But on the other hand, if the N1 is a better car than anything else you can find then why not buy it and treat it like any other gtr? sure you might anoy some of the purists but at the end of the day its you car.