Neat concept. To darken it, you can mess with curves and layers and burn out the background..possibly using different channels to turn it b/w would help with darkness as well.
Interesting idea and nicely done. In my opinion though your photoshop goes a bit too far and obscures the actual idea, might just be my monitor but I cant really make out the dollar at all anymore so the concept itself is lost.
I like the concept....... but i prefer the first version, the second IS too murky IMO..... it looks ok on screen but i think in print it wouldn't be clear enough..... so i'd go with the first..... and in the general gallery,.....where it would also get more views.