First off, I'm insanely jealous of your clear tails. Especially on a black ucf..
I think spoilers don't really fit this car. You can get away with a roof spoiler only because it looks like a window visor, only for the rear windshield.
All of this is totally subjective (obviously), I mean I'm not a fan of the whole slammed concept or movement. In fact, I absolutely despise how it makes the ucf's look. And trunk spoilers fit in with that ideal. Then again I'm not a fan of the total opposite of the slammed look either. Huge donk wheels and tacky paint jobs, not for the ucf's. No sir.
I'm not a fan, but if you liked what you've seen from other ucf's with a rear spoiler, then go for it. At the very least, you'll get to see one in person if you do it to your own car. I can't tell you no, because I plan on some doing some cheesy mods to my own car for the same reason. To see if it fits the ucf's own style, subtlely.
That spoiler is OK, I guess. I mean if it came with the car, It wouldn't kill my feelings for the cars beauty.