Production is essential to the mix here, we tried the concept of simply driving an economy by selling each other non-produced things (typically services, like mortgages and loans) and you saw what happened there around 2007/2008.
An economy cannot be spun out of thin air, we need to sell stuff to each other - sure, but we need to sell stuff we need to buy and make sure its regulated so we don't go into another spiral of 'profits' generated out of our imaginations. After all, my house is worth a million dollars, so I'm incredibly rich.
There is an issue with investment - as you noted. As the rate of return drops due to too much investment money chasing yields, investors demand more interest-bearing investments, which is why housing (as 1 example) has gotten out of control. Instead of investing in productivity, they are simply inflating a bubble (again). This can't be healthy for an economy.