It would be better of as a demo rather than a fully priced game.
The good stuff from GT3 is in there, and that is about the end of the run for this game. The only difference I see is the inclusion of cars revealed in the 2002 Seoul Motor Show. It does introduce Hyundai into the Gran Turismo family. The selection sounds sound the same, again, and the cars sound the same, again. There is so much recycled content that if GT3 was released on the PS3 with full PlayStation Network coverage, then these games would be far better off as downloadable content. I don't know, I'm just saying.
In conclusion, Gran Turismo Concept 2002 Tokyo-Seoul is not really a game worth playing, and buying Gran Turismo 4 is far more worthwile. Don't waste your money on a game so short you could complete the whole thing in about 3 days.