Then you concede that the effect from merchandise trade is contractionary
It depends what the net effect is. If the currency circulates abroad then it is contractionary in terms of domestic prices. If the currency is repatriated immediately, then it isn't. Since the Yen isn't a reserve currency, I would tend to say it isn't. The US, for example, has managed to export its inflation, and that has been opportunistically contractionary for US prices.
It seems you make an elementary stock versus flow error. The effect on the income from the existing stock of net foreign assets is overwhelmingly dominant in a scenario where the yen suddenly appreciates a lot. You might as well say that after an earthquake, construction firms will be able to jack up their prices and therefore boost spending.
No, I was referring to the fact that financial assets abroad will become cheaper in real terms given a Yen appreciation, but I agree that existing foreign income will become cheaper, and I agree that this would be more influential to a Japan that is dominated by foreign investment. However, this situation, much like the cost of exports, would drive the Japanese not only to consume more domestically, but to invest more as well. In fact, this is what is happening now, as we see the Yen carry trade wind down in favor of a US dollar carry trade going forward.
While you identify the pro- and con- forces operating, you are confused about their comparative impact.
I disagree of course, and I think you've expressed a strong bias towards inflationary monetary policy as it concerns foreign exchange rates. Big surprise here. Frankly, I don't care whether exporters' costs fluctuate as a result of weakening or strengthening currency, exporters and exports make up a small percentage of any economy (roughly 9% of GDP in Japan's case, apparently). Deliberatly weakening the Yen hurts the purchasing power of people who own Yen and Yen denominated assets, period, and it hurts more people than a strong yen hurts exporters.
