I'll agree with jr on this one
The 92-99 model had a trunk lid that sloped so far down. The style is very round, and it looked like it just dropped off to the taillights.
The spoiler adds a nice change in direction and introduces a linear element the downward slope. In my opinion, anything more then the original "design intended" spoiler is too much. But to each their own.
Now on the 87-91 model, the trunk lid is horizontal, and you already have that linear element in place, a spoiler is a nice feature, but you can survive without it.
(my .02 cents)
Diamond White Classic Aurora - Back on the Road
Galaxy Silver Grand Prix GTP CompG - Soon to be mothballed