I for one am not anti-spoiler, but maybe it could be said that I am more for originality - Once you start modifying an original car, it's really easy to keep that ball rolling...
I used to vastly prefer the spoiler look, but I have come to appreciate the lines of these cars without spoilers;
I also love sleepers.
It seems to me that the spoiler tends to give pretty much any Firebird a bit of a 'Trans Am' vibe, and while the spoiler tends to disrupt the flowing lines to a point, it also kills a bit of the sleeper look.
Let's see if I can explain it another way;
I love the Muira, that car is all about the body lines;
A Formula (or lesser models) with out any spoilers to me exhibits some of those same characteristic flowing lines that I love so much in the Muira - the forward facing scooped hood to me, adds to the aesthetic without disrupting and body lines, but rather complimenting them.
This might seem a stretch for some, but maybe others can see it...