It's a difficult car to value, in my opinion. I've always found prices to be all over the place.
There are so many factors, and with it being a car where options do actually add value & desirability - people tend to reflect this in their asking price.
Mine was bought in 2012 at 47k for £12995 from VW - strong money at the time, but mk6's were stupid money. Today, I wouldn't change my mk5 for a mk6 - the gti isn't special enough in comparison, but an R would be tempting. Mines currently on 66k, and if I were to sell, it would be up for at least £9.5k due to condition and specification.
As the cars get older, it's all about condition and history, IMHO