The system you advocate has great merit. I don't have a perfect plan in mind, but trust the good folks that have done such a marvelous job of creating a worlwide phenomenon could implement a rating system that takes MOST of the guesswork, subjectivity, and "reading between the lines" out of selecting candidate caches to hunt down.
I can't imagine a scenario where some system would not be better than none. The idea here is not to rate caches by difficulty, but by a criteria which includes location, container, contents, uniqueness, cleverness, etc. The ratings could be anonymous and impersonal.
In time, the trend would be toward more rewarding caching experiences, and rewarding a cache owner for some extra thought and effort with a high average rating will help us all.