It's like this plain and simple (IMO).
My first bike was a Trek 1200 Aluminum frame $800 I think
My new bike is a Trek Madone 5.2 full carbon $3500
Advantages
1.) 5lbs lighter
2.) Better components
3.) Better ride
4.) I can say I ride carbon (yippy), show, OCP points, blah blah
Disadvantages
1.) $$$$$ 4times+ more
2.) The guy I sold my bike to rides with me twice a week
3.) More to worry about when crashing
4.) Not really faster, especially on flats around here
5.) Components not noticably better, shifts the same, lasts just as long but more $$$
Worth it?
Maybe, if you have the money and status is important to you. If you ask me, it's a lot of hype and money for not that much more bike. It's kind of like computers, once you go past a certain point, you are paying a lot more $$$ to get the cutting edge of technology when you can take 2 steps back, save a lot, and not notice a bit of difference.
Seems to be a status thing really...
JMHO
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~willieb