While I don't buy your economic analysis - I think it would have a major negative impact on productive investment and economic activity - I came to a similiar conclusion years ago. The effects of any one-time payment would disappear within a generation and probably leave both Blacks and the country in worse condition, both economically and spiritually. The failure of the reparations program to lift people permanently out of dependency would leave resentments.
People with little experience handling money (think teenagers) would fritter it away on luxuries. There would be a boom in "African Heritage" travel packages, luxury car sales, wide screen televisions, "urban living communities" - you get the picture. Hucksters of every hue and stripe would cash in (think myriad Al Sharptons). The economy would starve for productive capital. France would surpass us in GDP. And everyone, Black, White, Other, would remember and resent it for another 10 generations.
Maybe I should write a book "How You Can Profit From the Coming Reparations Movement". Print glossy brochures offering "African Heritage Vacations", market "authentic" Africiana, invent African-themed investment schemes, think of the possibilities.