CTFs really are what you make them (like a lot of other things in life).
Networking You never know who you are talking to at these events or what type of opportunities arise with the people you are working with. You never know who will notice your skills at those kinds of events either. You may start a company with people on your CTF team or meet someone who offers you a great(er) job.
How it looks: I put victories for some of the CTFs Ive done on my resume (I guess Im the different kind of security person bethlakshmi mentioned :-) ) and this is almost always what potential employers ask me about.
Usually they ask questions like
1) What did you do for your team?
2) Did you ever work with
technology they want?
Usual interview questions, but they honestly want to hear about the experience and can use it as a way to validate "This guy actually knows the things that are listed on his resume".
I would also say that breaking imaginary TCP services and funny puzzles are important to being a good pen-tester. People who have the skillset to break those puzzles understand not only the how to pen-testing, but also the "why things work" behind pen-testing. Potential employers will see you as being more eager to solve new problems, yada, yada.
Answer Is it for you? I guess you will have to try it. I can tell you it is a great way to have fun, make new friends, and learn more security. At the very least you will have people on your team who will help your pen-testing skills grow. In my opinion its worth it. For career advancement...that really depends on where your career is today and where you want it to be tomorrow.