Understanding Aggadah (Allegory)

Rabbi Israel Chait

I recently asked Rabbi Israel Chait how to understand the "miracles" of Rabbi Chanina Ben Dosa found in Talmud Taanis 24b-25a. I asked Rabbi Chait as follows.

Student: If Revelation at Sinai is the barometer by which we accept miracles (mass witnesses is necessary for proof) does this force us to interpret all such Talmudic accounts of "miracles" as metaphor when masses were absent?
These miracles (one was where vinegar burned as oil) seem to surpass the miracle of Channukah. 
Furthermore, we do not see such miracles performed for King David or King Solomon. Are we then to say that Talmudic Rabbis – who are not prophets – benefit from miracles, while the prophets did not? Meaning, do miracles occur, despite the level of the recipient?
The stories (24b at bottom) open by teaching that Chanina Ben Dosa was poverty-stricken. No miracle helped him find success. Yet, a "miracle" occurred when his wife had no bread Erev Shabbos. She burned twigs in the oven (smoke exited the chimney like one who is baking) to make it appear she had bread so as to save face from her neighbors who did have what to cook. But when her evil neighbor – knowing she had nothing to cook – walked in to inquire of that smoke, bread "miraculously" filled the house.
Certainly the "miracle" of his goats balancing bears between their horns is not literal. And Rambam and others teach that Aggadas are not literal. 

What is the rule by which we determine when Talmudic stories of miracles are taken as metaphor?

Rabbi Israel Chait: To paraphrase Shmuel Hanagid(1), the value of Aggadah (allegory) is found only in the gems of wisdom one derives from it. If one derives nonsense, it has no value. Very few people are capable of 'diving into the deep water and coming up with pearls'. [Ramban metaphor] Other individuals have no business delving into Aggadah. They would do better refraining from trying to interpret that which is beyond them. "Bmufrosh mimcha al tidrosh". Such people cannot discern between something literal or metaphorical, so your question is moot.

(1) See "Mavo HaTalmud" (Intro to the Talmud) found at the end of Tractate Brachos