I've never paid $6000 for a bike (geez, my used CAAD10 frameset was $375), but lightness is a real world benefit. Some people have an almost ideological commitment to the idea that weight doesn't matter. But duh, of course it does. What real world benefit do you get from being so delusional?

On helmets, I've liked the expensive ones I've had better than the cheap ones. First expensive helmet was a Giro Atmos. After that, I've had three Lazer Z1s, because I'm a klutz and broke two. I don't think I would buy them at full price, to be fair. But gosh, they're light, and the Lazer matches my team kit so perfectly. If you can get a deal, they're amazing. If you can't, today's inexpensive helmets are still pretty great.