I did all you noted above without success.
I just went ahead an uninstalled the WA extensions. Then uninstalled DW. Then deleted the DW CS6 files from my C-drive as it was still resident there. And then I reinstalled DW.
That seems to have resolved the problem completely.
Design Extender and Data Bridge work fine but eCart and Web Tools still have problems. I suspect that the issue is with an option to "Replace Newer Version Files" which comes up during the extension installation process. To date I have said "No" to this option. Perhaps I should have said "Yes". What say you?