The Greek we used today has a fun play on ideas contrasting "the one worthwhile" where the sense is "the worthwhile person" with the number "one." The phrase "one [number] is the worthwhile one [person]" could easily mean "any person is a worthwhile person" since the number "one" can be used as a pronoun, just like our "one" can to refer to a person. "One is valuable" could be one meaning of this boiled down.

The KJV source is different than the sources we use today, but the translation has elements that are closer to today's source, and not in its source.  The NIV version adds a lot to make this verse say what they think it means. This is a good illustration of how things can get changed around in translation, and how translators can choose one meaning or another. This is also a good example where a comparison between the Gospels is interesting, The Mark and Luke versions are almost identical to each other but much simpler, and in vocabulary, more like the KJV source. This version does not mention "God."

The rest of the story in all three Gospels is detailed and very similar, so we can assume that this question was answered only once. What is more likely: that the answer in Matthew, which is more detailed and ambiguous, was built up, or that Mark or Luke versions were stripped down to a simpler and more straightforward answer? I propose a third possibility, Jesus said both things, the longer version harder to understand version and the shorter and both were recorded or remembered, but that the Gospel writers saw no need to include both answers.  Mark and Luke preferred the simpler. Matthew, the more obscure. Perhaps Jesus said, "Why ask me about the worthwhile person. One exists as a person worthwhile. Why say of me 'worthwhile?' No person valuable if not one divine."