I get what you mean about the RX7's but they had a small fin built into their trunk line unlike a Trans Am. Something about the T/A's looks like its drooping like saggy T*ts.
RX7:
T/A w.o spoiler:
Sunfire:
Second Gen T/A:
Camaro 3" Spoiler on a T/A:
If you were able to incorporate a small "Flip/duck-tail" spoiler into the trunk it might able to be pulled off.