First of all, I think with some small changes it would be a fine, solid UI. Nothing fancy, just solid.
So, why do you use two actionbars for mounts? You could try to use a hidden one or just something like
FlyoutButton.
I, personally, would swap the position of your XPerl frames (why do people use XPerl..) and your main action bar.
I don't say much about the HUD, 'cause it wouldn't be something nice, dunno. Personal thing.
Then I would try to hide most of the useless minimap buttons. I mean SexyMap has mousewheel zoom, so why +/- buttons?
Same for Prat. Hide the buttons and change the tabs.
Like Phanx said, try to make the AddOns look similar, with fitting borders, fonts, etc .. so that it does not look "throwed in".
The black bar. I mean. Okay. It's kinda ugly, but ... do you use any kind of viewport addon so you don't loose a sh*tload of view? I knew some people who just put a black bar in there w/o changing the viewport, so just asking. *If* you need that bar, try to make it look a bit more.. appealing.