While I understand - though disagree with - your frustration, there's a better method involving license tests already posted in this thread.
I have all the bronze and all the silver prize cars for b, a, 1c, and 1b, and there are at least 3 or 4 races in beginner that I don't have cars for. All gold on "b", btw.
You are suggesting I need an all gold license prize car from a, 1c or 1b, or I need a a level 12 (1a or S) license prize car just to finish the beginner races?