As far as I can see the mk4 R32 didn't take the huge hit in depreciation in its life that the mk5 has. A nice mk4 R32 isn't that far away from mk5 money. Which considering the age difference is pretty impressive.
The mk4 was an outstanding car against its peers, which at the time of lauch was whatever astra was 3 or 4 generations back and the ford escort! Compared to them the mk4 was absolutely light years ahead and is still desirable and fetching £k's rather than the couple of hundred you would pay for the equivelent escort or astra. Cabin quality was (and still is) class leading and very close to audi quality.
The mk4 gti's were a bit of a lazy effort on VW's part but the mk4 as a whole were and are still are brilliant. The 1.8T is a fantastic engine and is practically bomb proof. Its easy to slag something when you've moved on but credit where its due they are still fantastic cars.