Everyone gets different enjoyment from bonsai, let's not knock one way or the other. If you like going to nurseries, buying inexpensive stock, and working it... fine! That's a great way to enjoy bonsai. Your trees will be very slow to develop and will take a long time to be breathtaking, but if that is where you most like to concentrate your efforts, then you are getting something out of your choice. If you like to buy stock that has already been worked, or specially grown for bonsai, that is also a very valid way to enjoy the art. If you can collect, that's great! If you are in the nursery business, and can import prebonsai stock, excellent! They are all VALID ways, and we each get our pleasure from the path that suits our personalities and our goals the most. There is no ONE RIGHT WAY.
However, most of the bonsai that I have seen in really good exhibits has been older than I am.
The trees are on their second generation of owners, whether passed from a family member; bought from an ailing friend; or donated to a collection. These trees have been in pots for forty or fifty years. It is absolutely acceptable to buy, nurture, and cherish these trees and value them just as much as one that you started from a cutting. Why would it not be so? They are living works of art, with a history and decades of love poured into their growth. To be a caretaker of such a tree is an honor. Because they are living things, even "just" a caretaker has to be able to maintain them and make decisions about changes which come when the tree outgrows its original shape. They can't afford to make a mistake... they have more than just a piece of nursery stock. They have a tree that has a pedigree.
I, also, went to the California Bonsai Society FIFTIETH anniversary convention yesterday. Think about that a minute. Fifty years, and many of the trees had been started during John Naka's heyday. (It was a club that he formed, and they are some of his original students) One of his own trees was there. I would take any one of those trees, any day, over the same value in nursery stock. Absolutely. And would savor being able to tend to it.
But those trees are priceless to their owners. They may have bought them, too, decades ago, from even earlier practitioners or from good imported Japanese stock.
Bonsai is about different things, to different people. To me, it is about the trees. (Not said at all sarcastically, but with reverence) It is about tradition, and beauty, and enjoyment of the blending of trees with the artistic insights of the people who tend them.
If you like to take nursery stock, and spend years shaping it, creating a new nebari, grafting branches where there is a lack, and growing taper, that's fine. It's fun, and satisfying, and interesting. But don't invalidate the experience or enjoyment of others, who are overjoyed to bring a tree to their collection that is beautiful and old.
If you like to collect from the wild, and enjoy nurturing a tree that was whipped by rain and wind, that died down during drought and that was nibbled by wildlife, then your enjoyment is a different experience than that of the city person who has little access to wild trees. Collecting is valuable, and is a great suppliment to the bonsai world, but it is also not the only way.
If you like to buy good stock, that has already been started, and improve it with your own vision, then your journey is down a different path. You value the grower's work and care, and you carefully select the trees that you feel are worthwhile. Like the nursery stock grower or the collector, you are getting something out of your journey that is particular to yourself.
Joanie