I get the exact same feeling all the time. After nearly 12 years of Security Penetration Testing I still go on-site thinking, "Shit, do I really know what I'm doing? What about all the cool young kids posting all these wacky papers on technology? What if I miss something? Surely it's not that hard to run a set of scanners and root an insecure box?"
I used to try to contribute to the community but I don't have the time anymore and a lot of the time I'm contributing to people who's employers we're in direct competition with (and we've had said competitors after invite only conferences trying to pass off my research as their own).