Well, a problem with the theory in general is that the private spending of the upper class is the not single driving force of the economy. The mass consumption of the public, namely the middle-class and poor, is indeed a major factor but also the spending of corporations is a huge factor as well. When the wealth is concentrated at the top of the market, in the hands of only a few, the problem is not that they buy only a small amount of goods. Rather it's that the corporation does not invest that money at all in its workers or in expanding its plants in the United States. Companies do what is economical and they take their surplus profit and reinvest it in research to further lower their own costs by laying off workers, using temps, part-time employees, relocating factories to lower paid portions of the world, using more technology and in general doing everything they can to increase their profits. If your workers are already working for say 6.50 an hour, why would you give them a raise? There is a surplus of cheap labor in the service industry.
Indeed with the "trickle" down economics that was set in place the US economy did see a growth, as the rich got richer. Companies gained a great deal of money, but you can also look at the sudden craze of outsourcing jobs. Entire factories uprooted and moved after this economic philosophy came into place. The original thought behind "trickle" down was that the money would do as Nightbird is suggesting and the CEOs would invest their profit into the workers, giving them more pay. This simply does not happen and forcing them to do so won't work either. A great deal of the United State's problem with social reform and welfare deals with their perception of it and what they feel people have a right to demand. Perfect example is Social Security. Before "The New Deal" there was no retirement age or social security, you weren't entitled to anything. Now people feel it is their right to demand social security checks when they retire. A complete change of perception. Currently people believe that the poor are lazy, criminal, uneducated, and want nothing more than free handouts. This does not promote the public to care.
Ironically people do feel that companies are justified in asking for welfare, yet poor people are not. The United States has invested billions in many of these corporations in the form of money, tax breaks, tarriffs, military manpower, diplomatic weight, legislation, and providing them with insurance (money given to airline companies after September 11th). They feel that these comapnies should get these incentives and forms of welfare so they will keep their jobs here and expand, improving our economy. So instead of viewing welfare as a way to promote education of its people and thereby improve the workforce, the United States believes that the money should go directly to the company in the hopes of them remaining here. What has happened is of course the opposite. The problem is very complex and intricate, tied into almost every facet of American culture and economics.