Ooh! Great topic premise. Here's some trivia off the top of my head:
1. CT is that in the original English translation, 12,000 B.C. is called the "Dark Ages," which wasn't in the original Japanese. I think this was a nice touch: It doesn't only refer to the Earthbound Ones or to the ice age; it refers to the Enlightened Ones' not-so-enlightenedness, implying decadence and repression...the seeds of contamination which ultimate destroyed the floating kingdom.
2. Crono is the only "ordinary" male playable character. All three playable females are regular human beings, but Frog is a Frog, Robo is a robot, and Magus seems to have had more plastic surgery than a movie star. (Honestly, I wouldn't even have called Robo a "male" until they made it painfully obvious by pairing him off with a pink robot who wears a ribbon.)
3. Crono's theme and "Corridors of Time" are structurally very similar to one another, yet I've never seen anyone else point it out. Indeed, many songs within CT are structural or thematic cousins, such as "Ocean Palace," "Manoria Cathedral," and "Battle with Magus" in one group; "Guardia Millennial Fair" and "First Festival of Stars" in another; and numerous songs relating to Crono's theme. Across the games, "The Frozen Flame" is related to "Ocean Palace," as is "Ancient Dragon's Fort" (less obviously), while of course Schala's theme more famously makes a brief but unmistakable appearance in "Life - Faraway Promise."
4. There is no "child" sprite for the average citizens of the Kingdom of Zeal--the only place in the game where this is true.
5. Gato's theme shows up as a battle sound effect in combat against monsters who bear his likeness.
6. The regal color scheme of the Kingdom of Zeal is orange and violet. Queen Zeal, Dalton, and two of the Gurus were all depicted in the official artwork to wear these colors. Gaspar was depicted in his End of Time garb in the official artwork, so we never got to see his Guru attire. In the sprites, there is far less consistency--probably an oversight by the sprite artists. (See: General Leo.) Additionally, Schala and Janus wore a softer shade of violet, and no orange, perhaps indicating their regal status but also their lack of high office. (That's speculation on my part.)
7. I'm not the first one to point this out, but I always get a kick out of it: Belthasar, the Guru of Reason, ended up going insane. Melchior, the Guru of Life, designed the Mammon Machine and later built weapons for a living. And Gaspar, the Guru of Time, wound up thrown outside of time altogether.