Since I had a go at sharpening this image, I have purchased a plugin called
FocalBlade which an absolutely excellent tool for jobs like this. It has several different modes from Novice to Expert and literally dozens of independently customizable settings that allow you to get just the sharpening you need in just the areas that need it. It's compatible with both Windows and Mac, and at only $49.95 it won't break the bank either.
I just realised I'm starting to sound like a salesman so I'll shut up now. Check it out here:
http://thepluginsite.com/products/photowiz/focalblade/