I think what you might note if you start really studying Chinese and Japanese furniture that are used for bonsai stands is that there is rarely a simple, flat board surface unless it is the center panel of the stand.
The solid surface vertical you have there has too much visual weight and it blocks light from hitting the tree from one side.
I would suggest that you make the vertical surface more of a suggestion of a cliff rather than an actual representation of one. A single thin line rising in a bit more off-kilter way would be more evocative to me than a large plank of wood. You see this same idea in a 1/2 moon stand design.
This stand was never designed to copy Chinese or Japanese furniture. There are plenty of people making stands like that out there. I just wanted to design something a little more American with a nod to the aesthetics of Oriental design.
I agree the back piece may be a little heavy handed in that respect. But I do like the height and the angles it creates, and like I said earlier, I also believe it needs the weight it creates. To me, it isn't that high that it blocks any light, but gives a feeling as to why the tree is going that way.
I never made it thinking everyone would like it. I've been doing bonsai long enough to know that would never happen
But a couple of times at our show I noticed people looking at the tree and stand, and from afar and you could see that they were discussing the angles and such, and that made me happy.