I500 is one of those games that isn't terribly deep, but the modes are extremely well integrated with the theme. The custom voice work by Paul Page, Bobby Unser and former track announcer Tom Carnegie (RIP) is first rate. There isn't necessarily a wizard mode, so once you achieve everything, the Victory Lap is a bit of a let down but on the whole, the game is a lot of fun.
As others have said, at 2,249 units, the game is fairly low production so they are somewhat rare. When the game was first released, I had the good fortune of having one at a local restaurant/bar and played it every day at lunch. A few years back someone posted one for sale on rgp without any cabinet fade and I picked it up for a fair price. I do think the theme is a bit of a factor as well. The public interest in the 500 isn't what it was 20-30 years ago when you had guys legends like Foyt, Mears and Andretti racing.