I thought that spoiler looked awful. It was way too high and the side profile of the trunk and wing didn't even come close to matching. They actually intersected. The mounting pillars needed to be chopped and angled so it would lean back. I think the only ones that work for a 3rd Gen are the Z28 style that are somewhat integrated into the keyhole portion of the trunklid.
First I want to remind everyone that this is an open forum. If ask for opinions, your going to get them. Not all taste are the same. Not everybody agrees on everything. In the end, it's you car and you are free to do what you want with it. That said, here is my opinion on rear spoiler on third gen Novas.
I've always been a form follows function kind of guy. If I add something to the car, it needs to do something to improve the car. A rear spoiler is supposed to (by design) add more down force to the rear of the car. If properly designed for the application, it will help keep all four tires planted firmly on the ground. A poorly designed spoiler or the wrong one for the application could have a negative effect.
Too little down force and you see no benefit. Too much and the front end gets light. The large wings on most of the ricer cars would be best suited to 1/4 mile racing. They tend to direct the car in a straight line and make cornering at high speeds difficult.
NASCAR, auto manufacturers, and pro racer teams spend countless hours and dollars on wind tunnel test of spoilers of different sizes, shapes and angles. I, personally, don't have access to those type of facilities nor the time to devote to research and development. I haven't talked to anyone who has developed a rear spoiler for a Nova. I figured out a long time ago that a Nova is not a aerodynamic car. (A third or forth gen Firebird would be a much better choice for aerodynamics.) I chose an X-body because I like the basic shape of the car. I prefer clean simple straight lines. That is why I prefer no rear spoiler or crazy bolt-ons on a Nova.
"The Fast & the Furious" movie perpetuated the myth that a rear spoiler makes cars faster. It seems like everybody under the age of 25 wants one now. It's a trend. When the trend is over, all these cars will have holes in the rear deck. Anyone who has ever done a restoration would have to cringe at that thought. I bit my tongue on this for a while because I was young once. Now I wish somebody had stepped up years ago and said something before we screwed up all those perfectly good cars.