I've been to Japan (winter '03 - '04) to visit my in-laws. It was in Fukuoka though, not Tokyo. (I live in Europe). But it's really like being inside Gran Turismo. I didn't look for Skylines though, but I'm sure they're there. But many cars are like, lowered, with wings, and loud exhausts, and the wheels of ALL the cars are either racing-type or chromed. Also there are many futuristic designs which only reach Europe much later like the Nissan Z, Mazda RX-8, Nissan Cube, Toyota bB, I've all seen em there. Also classic cars are so well preserved they really look brand new. I took lot's of photo's and I will start a thread with them but I don't have access to them untill a couple of weeks from now. On itself, the cars aren't THAT special but it's the frequency that really amazed me (e.g. every day I saw at least several Toyota bB's). I'll be visiting Japan (hopefully) every winter, so I'll be on the lookout for the GT4 fans that can't make it to there.
It's really worth a visit though!