I'm sure he's doing well, but it also sounds like he's a real automotive enthusiast. While $350-500k sounds absurd for a "car", if it is his dream, with how well they've done, and his fees on speaking engagements... that's probably not that far out of reach.
Is it a good investment? In happiness maybe. Some of the best times of my life were taking my car out on the track. I miss it dearly.
After all the shit I've mumbled about him, 37s and rails... that he really wants this car--and appears to know what it is--his stock just went up a bit in my book. Us car guys, we stick together.
edit: Just saw someone else posting that it's more like a $1.5m-$3m project. That certainly changes the scale, but I still think the point applies.