My approach/attitude is; I go to Thunderbird shows to compete, and to local, "open" shows to display. To me, it's much more meaningful to show, compete, and win at shows where there are knowledgable judges, and standardized criteria for judging. Then, any award I recieve is meaningful.
As for local shows, my mindset is to dislplay, and raise awareness of the SC. As stated, there is no way to win against a Mustang owner who has all his buddies there to vote. And, that's fine. I have some really interesting conversations about my car with people who: A) Initially think it's a modified Thunderbird, then discover it's a (comparatively) rare factory model. or B) Previous owners who bought them new, sold them, and wish they had them back. I always hear "I didn't know Ford built these", or "I haven't seen one of these since I sold mine back in 19XX".
So, to answer the question at hand; at Thunderbird events, I enter the appropriate age bracket, and compete to win. At local "fun" meets, I usually go with "Late Model", "80's & up", or other similar class. It's not a "musle car". If I want to compete in that category, I dust off my all-original 67 R/T, and usually win : )
JD