I have judged and been judged at Corvette shows (NCRS) and there is always some degree of subjectivity. However they ALWAYS give the judging sheets out to the participants so they can fix flaws and do better the next time out. Doesnt mean the next set of judges wont find some different issues next time, but at least there are guidelines for folks to follow.
Note that it is MUCH easier to set standards when cars are restored to original than when everything is custom. On hightly modified cars pretty much everything is subjective.