While not an open source or QGIS utility, ArcGIS does have the ArcScan extension that can be used to help vectorize features from raster maps. ArcScan, of course, works best with 2 color images and hard edges, so I'm uncertain how the multicolor raster you showed would work. While it is not perfect, it may be another potential option.
Of course, as @Peter Ivan suggested, you could always turn to a 3rd party vendors, like Amazon Mechnical Turk (see more generic details as described by wikipedia), to digitize the data for you.