Not just watching it - I get involved: I'm not only a fan; I'm a race marshal, occasional pit/service crew, sometimes-competitor, race organizer... I cover the whole spectrum.
In a practical way, it really is a community, much like religion is. Maybe not so much as a fan, but definitely when you're directly involved. For instance, one marshal I work with was diagnosed with lupus a few years ago; within a few weeks of her letting people know, there were several teams sporting stickers on their car for a local lupus charity, and the next year, an annual fundraiser for lupus research was started.
Really, the main difference between our communities and religious communities is that our Sunday gatherings are a lot louder.
But as for the "spiritual" aspect, well, I think that racing is a powerful metaphor for life. It's very seldom that a person can truly find and push their limits in everyday life; racing is all about finding those limits and staying as close to them as you possibly can. I think that experience is tremendously profound, no matter what the context. To that extent, it doesn't really matter whether it's a
car that lets you acheive this - auto racing is just one means (but a very effective means) to communicate the idea that what we consider our limits are often not limits at all.
Also, there's the experience of racing itself: when you're actually in the car and everything's "clicking", you end up in a state that's a lot like a mystical experience... or at least how I hear mystical experiences described. It's hard to explain, but it feels like simultaneous complete control but also complete detachment... focus and attention on everything around you, but also complete lack of focus on any particular thing. It's very powerful.
Like I said, it's hard to explain... still, it strikes me from all the discussions in other threads about the role of mystical experiences in shaping religion that many religions have been founded on less.
Actually, if you're really interested in it, the best expression of what I'm talking about that I've seen yet is Eric Bana's documentary "Love the Beast". His view isn't quite the same as mine (and a lot of the movie is about love of cars in general rather than racing in particular), but I think it does a good job of expressing the feeling.
It's on TV occasionally, and you can get it at the video store. You can also find it online if you look for it, but I'm not going to post any links for that.