One on one access to Apple engineers is the real benefit of going. All the videos are free online for Apple Developer Program members.
Registered developers can already submit code level problems[1], there are official developer forums and bugs can be filed with Radar.
Meanwhile at WWDC, it's a developer scrum to get a 15 minute slot with an engineer and walk him/her through code they've never seen before.
From my experience, engineers do their best but they have always looked somewhat tired, hungry and distracted. All things given, I'm not sure it's the best environment to solve non-trivial problems, although it is nice to put a face to a name.
I've always had an easy time getting access to engineers. I hear a lot of people don't, so it must vary a lot depending on what topics you're after.
Maybe I was lucky. ~One year ago I had a problem with one of the Apple frameworks in conjunction with sandboxing and filled a DTS request. It took some time but the guy that I had contact with was very competent - so I guess it was an actual engineer. That or your average DTS intermediary will talk about disassembly listings with you.
Yes, the process was pretty slow but it was not painful IMHO.
Coincidentally I had asked in #macdev on freenode first and was greeted with some snarky remarks how I must be wrong as the reviewers know what they do ...