Quite a nice UI you've got going there. I agree with most of the comments which Seerah's posted though - the party frames might make a healer's job slightly more difficult since they're spread out.
I agree with you about having vertical HP/mana/rage/energy bars which would enable you to get rid of the HUD which in my opinion clutter up the screen.
I personally prefer an extra few buttons in my own setup - I would include another bar myself - maybe by just shrugging everything up slightly, making the XP bar a little bit thinner and moving the fubar items somewhere else (but I'm not sure where at this time).
I might be tempted to make the player and target 3D UFs slightly smaller and then, I'd be able to move the stance bar directly underneath the player UF which would make some space for the 3rd button bar I mentioned before
Other than that, I really like your UI! Keep it up! Just out of curiosity, what resolution are you using?