Sure I would buy a finished tree/tree that fits the "proper" bonsai pot it's growing in, and I would be happy to have it.
Would I consider it "my tree"? Sure -- after a few years, during which I've cared for it, developed it further, made my mark on it.
Would I prefer to "grow my own"? Sure -- but I might not have the time to do that.
Why do I do this? I love it! No matter what activity that is bonsai related.
Background:
As someone who enjoys working with bonsai, I'm only four years old. (Physically = white hair, retired, etc.)
For two years I killed every tree I worked on (stubborn know-it-all that I am). Well -- almost all. I still have one of the junipers, the first raw material I learned on. I have a fond spot in my heart for it, but I really miss the others.
At this point, I've gotten better at handling what I'm comfortable with, I have about a dozen plants in the ground growing out, I have more in grow pots, and I lost only one to our unusually harsh winters in the last two years. I even have a few trees in "real" bonsai pots that I'm not embarrassed for others to see.
On top of that, I am now very happy to care for two of our club trees. I'm sure they look better now than they did when they came home with me.
What a joy! Every part of it!
I love taking something common and unattractive, and making it something beautiful to see. I used to tell my students that art is what separates us from the other animals. (That might not be true, but I like it.)
I enjoy fully the day-to-day work involved in maintaining all the trees on my benches, stands, and flower/vegetable garden. My one-year-old shimpaku, my baby JM, my workshop JBP, my thirty-year-old Satsuki, my seedlings, my developing penjing -- all of them!
When I get a little frustrated by the lack of "finishing" I see in my personal trees, I remember how far I've come and I'm excited all over again.
And when I take the time to stop what I'm doing and actually look at what's there? I'm overwhelmed. By the babies in the ground, by the developing trees in pots, by the few that wouldn't embarrass me if others saw them, by the club trees.
Do I want more? Absolutely!
Would buying a "finished" tree make my day? Probably not.
Would I claim it was "mine"? To my wife, right away; to my children and friends, later; to other, a few years from now.
But I would absolutely do it. And enjoy it just like I do the trees I have now.
It would just be another facet of a hobby/artistic endeavor/activity that I truly enjoy hours every day.
Jim