I love the look of the left side, but the right side still needs some work. I would try adding a Crypt or two to the mid-ground of the right side, and some Java Fern varieties towards the back and the right wall. Maybe stick to windelov, phillipine, and trident java ferns as they tend to grow lower, and your tank isn't that tall. That should give you a nice contrast and help you get that darker color you're looking for.
Personally, I love Buces; I think they're beautiful. They're also relatively easy to keep. But most of them are really small, and they're all such slow growers that I don't think you'll achieve much of a visual impact with them, even in a 12g. They definitely won't hurt, but also with all their color and leaf variation, they may not fit in aesthetically, you know? Also, if you are going to use them, they grow best attached to a lava rock, or at least some kind of stone. I noticed that it looks like you didn't tie them down, but maybe I'm mistaken. Either way, especially considering their price, it's probably just not worth it to use Buces for this scape. If you decide to take them out, you can always sell them, or better yet, grow them emersed. After all, you're going to be deconstructing several tanks so you'll have some space and lighting already, and pots and dirt are cheap.
Just my .02