Agreed the Sat Nav is aftermarket as it is MY 2007 (MFD2 with silver buttons available on late 2006 GTI's), but it is a genuine VW part. Sharks fin aerial looks genuine as well. Steering wheel appears to be from an Ed 30, but again a genuine VW part. Car looks to have been sympathetically updated using genuine VW parts and that's no bad thing.
DV probably failed or replaced as preventative maintenance, so that's why it has been replaced. It's a known weak point in the GTI and a basic 'performance' modification - most likely a Forge replacement item.
Looks/sounds like a straight car owned by an enthusiast but you need to view it and make your own opinion if you are interested in buying

Cass