bonsaimaniac, I'm new to Bonsai, but I have to say that now that I'm using proper potting medium, there is a big change in the quality of my trees. Although there might not seem to be much difference, try some different mixtures and you will see some considerable differences.
Knowing how to water is something that is underrated, but soil is very important too. If you have any question about the importance of soil in horticulture, just go to a university library and check out some soil science journals. At Penn, there are shelves and shelves dedicated to soil science and a lot of empirical data collected regarding everything you want to know about soil.
I think the difference between hobbists and masters is the understanding of the impact of soil on the tree. Of course I recognize I know very little about soil other than it is very important
