Back in the late 70s and early 80s the Super Silhouette race cars featured big wide fenders, big wings to create more downforce and wild paintschemes to attract attention. Of course this influenced the people on the streets as well, applying the same wild modifications on their cars themselves.
More interesting is this video from 1984 on Tsukuba where another Grand Championship race is preceded by a stock car race: most cars look like the bosozoku styled cars of that era!
Especially the Cedric 430 (fighting the big Pontiac Firebird) and the Mazda Luce Legato are very typical examples here. Naturally they were modified in the same manner as the Super Silhouette to squeeze more grip out of that bulky stock car body!