I just did a quick Chow test to see if there is a structural break in per capita GDP growth between 1935 and 2009 and there is not.
This is just a growth over time model (log GDP on time), and I also checked consumption and disposable income. If I did it right, there are no breaks - not even close. So you are right about Wallison, but one can't draw the opposite conclusion either.
I think in general it is difficult to draw casual inferences about macroeconomic data. More specifically, I agree with David that there is not sufficient statistical evidence to ascribe a cause to the relatively weak performance in growth after 1980. I do think rampant deregulation of financial institutions has been on net harmful (we seem to have financial crises more frequently now), but we haven't sufficient numbers of data points to establish that fact scientifically.
But it is also true that what Wallison wrote is demonstrably false. Life was not barren in the pre-Reagan years, and it has not been the land of milk-and-honey since. The evidence, limited thought it may be, is consistent with the idea that the New Deal was a good thing. On the other hand, Wallison wears very nice suits.