Just like with any other bass, some are good, some are not. Being made in Japan doesn't necessarily mean it contains ninja magic. For example, my first bass, a MIJ Aria Pro II made in 1988, had a plywood body. It still sounded nice, but it was plywood. Do some research on the models. It's no different from today with instruments made anywhere in the world, the lower end models will be cheaply made, the higher end models will be better made. Generally, a high end MIJ bass from the late 70's onwards will most likely be a very, very nice bass. It's the general consensus that, at the time, the high end Japanese instruments were better made than their US peers and, clearly, the arrival of high end imports spurred the American manufacturers to up their game. It does come down to the manufacturer and model, though.