Isn't it the case that a central bank primarily lends? In this case aren't they effectively paying banks to borrow?

Given 0% interest rates haven't led to desired economic investment and stimulus the approach of the ECB and BOJ seems like wishful thinking that "more of the same" will somehow create different results.

While it's clear the stock market benefits from the increased investment, it's not clear that this addresses the lack of aggregate demand in the economy (which as mentioned seems highly influenced by demographics).

Then again this is probably more about lowering currency value than stimulating domestic demand.