I tried to sell my GTi recently and I couldn't get rid of it. I initially put it up for around €1,000. After having zero interest for a couple of months I started to reduce the asking price incrementally until eventually after around 18 months I had it advertised for €350. Still no takers, so I eventually gave up and took the ads down. Also nobody would take it as a trade in for a new car.
In retrospect I'm glad, because I am now coming back to the GTi and I'm really excited about it, but it is interesting. The car is a 2002 AUM and doesn't have insanely high mileage or anything (around 130,000), but I still found it impossible to sell.
I wonder whether Mk4's will ever start to go the way of Mk1's and Mk2's in terms of value, or is the Mk4 just too common for that?
EDIT: sorry for derailing the thread, but it's an interesting point. I too think spending 300-500 on headlights for a Mk4 might be hard to justify... but that's not to say I wouldn't do it! That's the thing about being an enthusiast I guess - it's more about the joy that modding a car brings you rather than the value. Sure most decent aftermarket wheels (or even a decent set of tyres) will cost more than most Mk4's are worth (unless you start talking about R models of course).