This technique works well sometimes, too.
Duplicate the original, if the jpeg compression has also desaturated the image a bit , CTRL+U to open the Hue/Saturation dialog and bump the saturation up a little more than you need.
Then Filter>>noise>>median setting of 3-6 (depending on the image) is usually enough, then Filter>>Blur>>gaussian at about 2-3.
Then set the top layer to color.
TA-DA.