It's a good question. In the case of these nvidia cards, it doesn't seem worthwhile: If you're seriously mining for money and buying hardware, you're still better off buying the AMD GPUs. I don't know if there's similar room for improvement on the OpenCL mining code, but it seems like it gets more attention.
Maybe it's not worthwhile for Bitcoins or Litecoins, but how about the smaller altcoins for which a competitive advantage early on can have a big impact?
