From my understanding, anything that brings the back of the car closer to the Ideal Template, is a good thing. Since it is certain that the rear slope of your Tiburon is under the curve, (due to the fact you can see out of it) the spoiler may be helping.
As for the mirrors, they're mounted on stalks which is a good thing, the only way to reduce their impact would be to remove them, but at what cost? Safety should always be a top priority, and in traffic, them mirrors is gold. Also local laws can be a pain as to whether you need an outside side mirror or not, I for one don't want to give "The Man" any reason to stop me. (Thats why my car is painted flat black with Radar/Laser absorbing paint and my windows are tinted to 87%, they never see me...shhhhh)
