Hi Jay,
Since bonsai is an art that uses artistic elements of composition of not only multi-element composition (like tokonoma or other kinds of display), but also for the trees themselves, individual trees are (can be) works of art, yes. There is nothing really wrong with display of a bonsai tree by itself. However, the "art" of bonsai is "best" exhibited with other environmental or referential elements in an integral composition. This is how the tree is put into context. But bonsai trees by themselves are often cool works of art, too.
As to whether or not you should exhibit your trees, I'd suggest that you be firm and concise in your reasons for doing so. When you offer up something for an exhibit, you are offering it up for critique whether you like it or not. While bonsai does not have to be an exercise in quality or convention or good-and-bad, and can be simply a fun hobby, when you exhibit it, it is taken into the realm of "art" and will be judged as such.
Now, we all start somewhere and learn and improve and such and there is no reason that exhibited work has to be "finished" or top quality (heck, most of my trees wouldn't pass muster for many shows), but it will likely be critiqued - either officially or unofficially. Use the positive feedback as encouragement, the negative feedback as a challenge to improve or as a lesson to work on - or simply ignore it and pay no mind.
If you want to exhibit your work, great! I say go for it, but know that you have to leave your expectations for the "results" out of consideration. Go for it! My advice, anyway. ;-)
Kind regards,
Andy Rutledge
b u n j i n | d e s i g n ::
www.bunjindesign.com
zone 8, Texas