One-day workshops and training programs serve a different purpose from week-long conferences. One-day seminars tend to be tactical: focused on a particular technology or skill. Week-long conferences are strategic: offering opportunities to discuss broader topics, to network, to build community, and to further the craft of SA as a respected profession. Week-long conferences give you "vision".
There is always one thing that I learn that makes me want to shout, "Oh Damn! That just paid for the entire conference!" There are many little "ah-ha!" moments too, but there's always one big one. Also there have been many times when I learned about a new sysadmin tool at LISA years before it was popular: that's really helped me stay ahead of the pack.
Week-long conferences have a powerful effect, providing a much-needed opportunity to relax, and they provide a supportive environment where you can take a step back from your day-to-day work and consider the big picture. Attendees return to their job brimming with new ideas and vision; refreshed, motivated, and with a new outlook.
While Christine and I usually don't endorse particular products (and neither does our book), we can't hold back our enthusiasm for the LISA conference which is put together by the Usenix (The Advanced Computing Systems Association) and SAGE (The System Administrators Guild) organizations.
We get a lot of value from their conferences. In fact, we met at one of them.