Most of the wealth that was generated by the cotton/sugar trade was destroyed during the Civil War, so on a certain time scale there was definitely an affluence associated with slavery, but in the long haul it was a huge mistake and any benefit was lost. It's kind of like if you somehow got a $500,000 loan that you didn't have to pay back for ten years, but if it wasn't paid back at the end the repo man cuts your hand off. Having $500k is real nice and no penalty for the 10 years, but is it worth your hand?

I think the accounting would be complex but if you looked at America as a whole and the financial ruin of the Civil War, Civil Rights, welfare ,crime,and the ongoing race mixing process I bet you'd come out in the negative on slavery.