Well, overall thats a pretty darn nice UI imo. If I had to do anything, "symmetry is beauty" so id keep the player/target bars where they are, maybe slim them down abit. Remove any powers that are not a MUST have that can be single clicked when needed or just bind them with spellbinder so they dont need to be on bars themselves, and then condense/minimalize the powers you have left and center them under the bars, also follow suit with any skills/pot buttons you have.
Drop the chat frame down to the very bottom right corner so its touching the bottom and the right side to the edge of screen. Put the stat thing on top of the chatbox, then make the chatbox 100% transparent so its clear and you should have a good portion more screen open with the minimalist look.