First I learned a ton more than I would have sitting at the house. Back then the videos were only distributed to conference goers (maybe ADC members too), then they opened it up to purchase access a couple of years later, now it's free. In 2007 and prior really the only sources you had were the Aaron Hillegass book (which still sits on my shelf) and a handful of scattered blogs or examples around the internet. 2008 was the year of the iOS App Store and a huge shift.
Networking was a huge thing that I should have done more. 2007 only had Mac sessions, with a few mobile web sessions. Nearly every big name Mac shop was there, in full force. Most of those shops have had to send fewer people lately, but they are still represented. Plus tons of new companies now. You'll never know who you might end up meeting. They offer plenty of time and places to do that while at WWDC.
The labs are the #1 reason to go WWDC. You get to talk directly to the engineers in charge of the frameworks. Bring them your app, code, and any issues you are having. For some people this is worth the cost of admission alone.
If you are just going to sit in on some sessions, I'd stay at the house and save the money. If you are going to network, use the labs, plus do all the extras like Stump the Experts, Design Awards, etc then it's definitely worth going.