After reading your question I was going to suggest to move the Java Fern to the edges to the right or the left since it is a low level light plant. Maybe adding some low growing plants to the front...also to try to have different levels of height across the back, meaning either to have it tall in the centre and then taper it out to the edges or tall on one side and lower on the other, it would make it look less uniform....
Then I read This Old Spouses idea and really like it, I can imagine that in your tank.
It's a good idea to draw sketches so you don't have to mess around too much with the tank, but you could also print off a low quality picture of your tank and cut the sparate pieces out and rearrange them to your hearts content. Maybe there is even some program/software like this on the computer, maybe in "paint" (don't ask me, I'm just glad I know how to turn on the computer
lol).
Your substrate sure makes the colour on your fish pop! And those pebbles add something interesting to it, love it!!!