I agree with Paul on this topic.
Workshops are fine, but the time you spend with the teacher is limited, and you only work on what you bring. You might also see what can be done with the stuff others bring in.
I have begun going to a bonsai master's garden for lessons, and seeing his trees up close. And working on them. It's the closest thing possible to apprenticing in Japan w/o having to use my passport. I've learned immensely more by working on world class bonsai than I would ever have by just working on my trees. None of my trees are refined to the extent his are, but now that I can see treexs that are at the "next level", my trees are improving immensely.
The apprentices that are going to Japan are learning at gardens where the trees have been kept in pots for hundreds of years. These trees have been styled by many people over the years. This whole concept of "it's not my tree if I didn't style it" is simply an immature concept. If a tree is great, it's great. It doesn't matter if you styled it. Bonsai is a living art. No tree is static, they require maintenance, renewal, and refinement.
We Americans seem to think that bonsai trees are supposed to be kept "show ready" at all times. That's not the way they do it in Japan. Sometimes a tree might get too rammified to be sustainable. Or, to look good in the show, they pot it in a very small pot. Too small for long term health. The Japanese masters will determine several years in advance what tree they want to show several years from that point in time, and they will plan out what they want to do to get it "show ready" in several years. After the show, they may cut it back severely, or put back into a training pot, or let the needles grow long on a pine to let it restore.
You can't learn this stuff at a workshop, or studying on your own. You have to be there, do that. Experience it.
That is what the new breed of bonsai masters are bringing back from Japan today.