Depends on what you're trying to achieve I think. I worked on my own stuff for 3 years before doing YC and it was well worth it. My thoughts after going through the program:
If you have no product and no track record, it's definitely worth it.
If you have something working, but growth isn't amazing, it's a risk because there's a chance you don't get the absolute most out of demo day due to timing -- so one might feel what you describe. That said if you blow up later, I'm sure they will do a fantastic job of getting you to the people you'd want to meet with - eg. Homejoy.
But if you come into YC with good growth (like doubling in size every month) it is without a doubt one of the smartest things you can do. You will probably never have as much leverage as you get while going through YC.
If you have no product and no track record, it's definitely worth it.
If you have something working, but growth isn't amazing, it's a risk because there's a chance you don't get the absolute most out of demo day due to timing -- so one might feel what you describe. That said if you blow up later, I'm sure they will do a fantastic job of getting you to the people you'd want to meet with - eg. Homejoy.
But if you come into YC with good growth (like doubling in size every month) it is without a doubt one of the smartest things you can do. You will probably never have as much leverage as you get while going through YC.