Andrew Wilkinson's Zappos "Redesign" which almost consisted of just putting gradients and drop shadows all over the page would definitely be easy with this project too!

http://www.metalabdesign.com/zappos/

The completely hopeless cases tend to either require some big HTML rewrites or really laborious CSS.

In general, though, I thought of the same thing, and it might lead to an increased trend in these unsolicited redesigns.