Golf are always desirable cars, especially in GTi form. Over the past decade, we've seen a domino effect. For example, when prices for a Mk1 GTi got too high, people started going after the Mk2 GTi. Prices for these are now high, but we're not necessarily seeing a shift towards the Mk3 GTi. Perhaps because in the 1990s, the GTi wasn't actually the quickest car in the range - that honour went to the VR6. Only you can decide if it's worth spending the money to keep the car going - do you like driving it? Does it mean a lot to you? To give you a rough idea of Mk3 GTi values, projects tend to be about £400 while the very best seem to go for about £2000-£2500.