Lots of good points being raised about this topic. I think like other said, a couple important factors are the economy, that is people who are of the age that are into modding their cars don't have as much disposable income these days, and law enforcement crackdowns have had a chilling effect on the big motor builds.
A lot of the things people do to their cars can be considered trendy, and and trends come and go. What is "in" today (i.e. hellaflush, bike racks, whatever) is going to fade away and be replaced by something else in a couple of years. Time will tell. In the "performance" camp, things have changed over the years as well. What was cool in the 90's and early 00's, like big, laggy dyno queen turbo setups, has kind of transitioned into more usable power builds, area under the curve, streetable power. Technology progression plays a role in the builds that people do.
I would say that performance is definitely not dead, though. Look at the Texas Mile, and the kinds of builds that fosters. Plenty of 13, 14, 1500 whp builds on Supras, Ford GTs, Gallardos, GTRs, etc. I'm not saying this represents your average enthusiast, because these are very high-$$ builds, but they are definitely pushing boundaries, if you look in the right places.
I like those examples phryxis posted. To me they are examples of enthusiasts that love their cars, put in a lot of time, money, elbow grease or whatever into their project and it's something they can be proud of. They don't have mondo turbos and they aren't race cars, but they are doing very nice work with what they have. Taking the car you love, improving it in almost every way, is what hot rodding is really all about. The wire tucks look clean and as long as they're not hurting anything, I don't see where the negativity comes from. I'd bet a lot of those care are just as fast or faster than my NSX, and if they are done cleanly, props to them.
The car scene is so varied. If you don't like what you see, keep looking elsewhere, and you'll find like-minded people.
