I have been to so many GSBF conventions I have lost count. I looked at the workshops on the GSBF site and found that the best deal will be on Thursday with two teachers providing their own material.
First is Bill Castellon. Excellent teacher, easy going and will easily work with beginners. It is a workshop with other participants so don't expect to get a full teaching all for yourself, but you will get what you need to make it through the class with a decent tree. Workshop is $145.00 and there is a picture of the trees on the website
http://www.gsbfconvention.org/workshop.html
The other workshop is also on Thursday with Peter Macaseib, he is on this forum and goes by Maria Kapra. Personal friend of mine and an excellent teacher. I have never worked with Peter with him as a teacher, but I know his personality and he will make sure everyone with a passion for bonsai will not have a bad experience. There is also a picture of his trees and they are exceptional for the price, some trunks look to be 3 inches across and about 8 inches tall. His trident maple workshop is $250.00 and well worth the price.
As far as the rest of the workshops I was not impressed and a major reason why I don't do workshops at conventions anymore. David Nguy's workshop with California juniper looks good and there are a few trees in there that I would like to tackle. His workshop is variable priced at $240, $365, $490. David will expect more advanced students with carving and styling experience for this workshop but it looks like good value.
Silent observer is cool, though the info comes fairly fast and you can't ask questions if you don't understand something. Watching the demos is good since they will have a narrator which will give instructions as well as the artists using the mic once and a while explaining why he is doing something.
The best tool at the convention is to spend as much time in the display room as possible. If you go to the convention for multiple days divide your viewing experience into a few days. Use the first day to take it all in and write down half a dozen that trip your trigger. Come back the next day or several hours later when you won't be overwhelmed by the trees and study the 6 you pick out. Pay attention to the trunk, is it scarred or blemish free, does it exit the soil at an angle or come straight out like a telephone pole? Look at the nebari, is it well distributed or is there some missing in the back or a bulge there? Get down on your knees and check out the structure. Are the branches wired or not, do the wiggle back and fourth, up and down or are they straight? Write down the things that you find make the tree so pleasing to you. Its overall shape, health, conifer or hardwood, and size. Many people are drawn to smaller size tree while others are drawn to massive trees, which are more expensive (pots, soil, and starting material.)
Hope that helps.