What does investment have to with tax planing?
The real threat to the US economy is that slowly more and more banks will get sick of complying with US rules and just leave. You don't want NYC to move London.
And no one can predict when that may occur. (Or when China may stop buying US debt, which would have a similar impact, CMIIW)
China's bond purchases are nothing compared to the fed and China probably cannot have a long term effect on the US (worst cast interest rates will rise slightly - there's plenty of demand elsewhere) except by colluding with other world powers to shift the global economic center away from the US. Say for example China does to the US what the US did to Iran, with an equal economy size and faster growth rate, we're in deep trouble.