I don't think I can completely agree with the strictness of the dichotomy you're drawing here. The main problem is, where do we draw the line? We certainly can't leave it up to each of our individual fancies, or the Bible becomes more like a Christmas buffet where you can pick and choose whatever you like.
On the other hand, there's certainly something to say for that distinction. Just yesterday, I was studying 1 Corinthians 10 at a meeting with my church small group. Verses 7 and 8 read as follows:
"7 Do not be idolaters, as some of them were; as it is written: “The people sat down to eat and drink and got up to indulge in revelry.” 8 We should not commit sexual immorality, as some of them did—and in one day twenty-three thousand of them died."
The problem is that the story that Paul is referring to (Exodus 32:6) actually had "only" 3,000 casualties (Exodus 32:28). A later story with a different background has 24,000 people killed (Numbers 25:9). Both numbers don't correspond with the number quoted by Paul. Back in the 19th century, this led the distinguished theologian Charles Ellicott to conclude the following:
"The explanation most in harmony with the character of the writer, and the utterly unessential nature of the point historically, is, I venture to think, that either the Apostle quoted from memory a fact of no great importance, or else that he referred for his figures to some copy of the LXX., in which the numbers might be specified as here."
It appears that Ellicott also employed a category of facts of "no great importance" and of an "utterly unessential nature historically".
How can we know how important or essential information is? I suppose we need three things to get us out of this tough spot. Of course, we need biblical scholarship to familiarize us with the cultural context of the writings which help to understand the intended message of the authors. This can clarify what is essential or not. Unfortunately, there's no absolute guarantee of knowing which biblical scholars are pointing us in the right direction. That's why we also individually need the guidance of the Spirit of Christ as we try to understand the Scriptures (like the disciples on the road to Emmaus). However, our individual fancies might still lead us astray there. That's why we need the corporal wisdom of the Church (both today and throughout history) as a litmus test for the sanity of our own approach.
Wow... I sure went out on a limb there. Anyway, that's my two cents.