Yeah I can speak from experience here...
Thurs - Empty
Fri - Empty
Sat - A bit more crowded
Sun - Decently crowded
Mon - Crowded
Tues - Crowded
Wed - BAD
Thurs (Thanksgiving) - Crowded
Fri - BAD
Sat - BAD
Sun - Not too terrible
Mon - DEADEST DAY OF THE YEAR AWESOME!
I swear, when we were there for the wedding it was like some sort of locust swarm on Saturday and Sunday as people started arriving for the Thanksgiving week. I never saw the parks go from so completely dead to so crazy so fast! And then we went to BGT on the Monday after Thanksgiving and seriously, less than 800 people in the park. 500 of them were over the age of 65. It was probably our best day at BGT EVER.