The argument seems to be: By becoming another level of meta I would simply be redirecting the flow of money rather than producing value.

I would argue however then that the vast majority of those charities are inefficient and therefore not worth donating to. Hence by directing money away from them value is actually being produced by the reduction of inefficiency. Thus if I can reduce the inefficiency by more than my donation amount I doing more social good than if I were to donate to them myself. Additionally, if I convert people to become more rational they may produce value which would have been lost to inefficiencies otherwise, and that might total greater than my personal work would.