I finally figured out how to properly test WireframeSketcher with retina screen (It's my bad I did not do it sooner). The bad news is that there are issues, the most important being with fonts. The good news is that I'll be able to fix them in 2 months when guys at Eclipse.org will release a new update of their platform.
Until then the only fix is to disable retina display support and run WireframeSketcher in scaled mode. This can be done by doing the following:
Go into the /Applications/WireframeSketcher\ Studio.app/Contents folder
Edit Info.plist file and remove these lines:
Restart WireframeSketcher and you are good to go. I will also release an update in a few days to disable retina support in current version. Scaled version looks ugly compared to other apps, but if you have patience you'll have a proper retina version in 2 months.