The exchange rate of 360 yen = 1 US dollar existed in 1959, when I bought Nikon F from Japan. The Nikon F can not be described as a camera made of inferior materials. At the time the exchange rate was designed to aid in reconstruction and stability of Japanese industry and economy. Also, Japanese individuals could only take a very small amount of yen out of country.
Unlike David, I don’t recall any decline in camera quality beginning in 1970. There have always been cameras of various degrees of lesser quality to meet different consumer choices. In 1958 I was impressed by a friend’s Petri with low cost and features. Relative in Japan said “don’t buy it, save up for better quality.” I waited a year or more and got a Nikon F. So, different levels of quality existed before 1970s, 1980s. I don’t recall any decline in quality because of rise of yen, but Nikon, Canon, etc began to manufacture for different consumer choices. Refusal of Leitz to introduce an entry level Leica May have contributed to its demise.