Already appreciated

I don't think Paul Walker had anything to do with it. The Carrera GT was holding onto its value pretty well before he decided to ride shotgun to his own death. The car had a manual transmission, RWD, clean '90s-ish aesthetic, and a V10 which was fairly unique for Porsche. As such it holds it has a traditionalist appeal for people that love old-school driving experiences.

You might be right, but the price spike happened rather precisely after he bit the dust.

As for more content, the SLS AMG seems to be holding its value rather well, especially the Black Series models

The GNX's actual value is hard to pinpoint. There have been a two ultra-low mileage (under 1000 miles) examples that have sold for 80-110k at auction I'm aware of, but these things go for sale so infrequently it's difficult to estimate a true market value. The only other one I've seen for sale has been available for nearly 3 years at 99k and hasn't sold. They've definitely increased in value any way you cut it, but I don't think the six figure numbers are and accurate market reflection.

It's an extremely Niche car. Most people dropping that kind of cash would rather buy something more showy. People who would rather DRIVE one, would be more likely to buy a GN and modify it with GNX goodies for a fraction of the price.

It was initially reported to be one. Blogs ran with that headline, but it turned out to be a GN. Normies (including many auto journalists) rarely can tell the difference between the two and people who think they know something often call the GN a GNX.

GT500s are down to 30k for 2009 models, they were almost 60k new right? I think GT350R will be similar