Not according to latest Texas A&M study. "Our findings indicate postmortem aging did not improve beef brisket palatability...." Comparisons were made between 7 days, 21 days, and 35 days. Want the details check out the link below.
Briskets were smoked "Texas Style" and served to test subjects and judged on "overall liking, flavor liking, tenderness liking, and juiciness liking". They also performed mechanical shear testing to add and objective tenderness rating.