The way I see it, is with a 98 to 03 GTP, we are now talking close to a 20 year old car. To me the book value starts to become irrelevant at this point. It's not taking in the fact that a clean rust free low mileage 98 to 03 GTP is becoming hard to find. This is where supply and demand start to play in, Although I do not believe these cars will ever become a high demand collectible car, I do believe there is still a strong enough following for them that the really nice ones will and do get a higher price then book paid for them.