Can someone please elaborate on how (and how much) value attending this event adds? Is it geared more for helping you apply to YC, answer generic startup related questions etc? Specifically, I am selected in YC Startup school and will have to spend at least a day to travel to attend the session. Is it worth the extra time and money?
The people from YC (at least the few I've met) spend a crazy amount of time around startups and have a lot of insight into all kinds of random problems that startups have that they see from being so deep in the startup world, so if you can talk to one of the people from there who's in your general area, and you have specific issues that you're grappling with how to approach and how to avoid pitfalls, they might be able to add a lot of value pretty quickly based on having seen people go through similar kinds of problems.
If you just want to go to the general Q&A, already are around hackernews and are already in startup school, I'm not sure it would necessarily be worth a whole day of travel. The Q&A is necessarily pretty general, and you probably are already getting a good general footing from startup school, although I second the other guy's exception of if you're really good at networking, since there will be interesting people there.