Tax cuts to middle income taxpayers are far more effective to stimulate the economy then to the wealthy. With all the tax cuts to the wealthy we have now, the economy should be BOOMING! IT IS NOT!!!!!
Simply stating something to be a truth doesn't make it a truth.
I don't think I've ever heard anyone support the argument that middle class tax cuts would have much of an effect. The middle class doesn't pay enough in taxes to make a cut do much.
The top 25% (i.e. "upper class") pay 85% of the taxes. The remaining 75% pay the last 15%. So I'm not sure exactly on what basis you think that a middle class tax cut would do this stimulating.
Moreover, the middle class would simply consume such a tax cut by purchasing commodities. While that's nice for retailers and manufacturers (increasingly foreign as you regularly point out) it doesn't have much long-term impact. Once the money has been consumed, it's gone.
The upper class, by contrast, generally makes their money by producing things (making stuff, moving stuff, growing stuff). Tax cuts provide more capital for them to invest in what they are doing which creates jobs, higher profits and in the long term more taxes.