The first time they introduced the Eugenics Wars set in the 1990s, Spock called it the last world war. Pike in SNW elaborated that it was part of the escalating conflict that went nuclear as WW3 decades later.
transwarp
I'd say TNG mostly stopped exploring new frontiers halfway through season 1. Farpoint promised exploration, but soon the ship is ferrying diplomats and scientists and answering Federation distress calls. The worlds are new to the audience, but not the characters.
There was a spinoff pitched during TOS called Hopeship featuring M'benga. The pitch for NBC/RCA was that instead of introducing expensive colorful sets, they could stay shipboard and have expensive alien makeup and costumes.
A Quality of Mercy also showed Una in prison, and Those Old Scientists implied she's revered. Did sending that letter prevent Pike from recruiting her lawyer? Things are already not heading down the exact timeline we saw Ortegas alive in.
It's definitely an industry change. Frakes has talked about how when he directs an episode now, the show's director of photography tells him to keep the camera moving.
With one barely mentioned planet, this episode reframed the plot originally designed to hold together TNG, DS9, and Voyager.
Federation authorities insisted the DMZ colonies were recent and had been warned they were disputed territory. They painted a picture like Israeli settlers in Gaza refusing to obey their own government and leave.
But now we have a Federation affiliated colony on Setlik 2 a century earlier.
The UFP's failure to stop the Maquis terrorists always seemed like command wanted the war restarted with plausible deniability. Now the Maquis arguments are stronger. Ceding long-held territory is much easier to call abandonment.
TOS had a proposed spin off for him, which would have ended up about his brother (played by the same actor) as first officer of a medical ship.
It would be astoundingly different after SNW.
Boimler is prone to exaggerating and has strange perspectives. It could be some obscure holiday on a planet he saved, or a Starfleet tradition to commemorate just on ships named Enterprise. Or there's another major holiday which coincides with Pike's birthday.
He reacted as if it was an actual Federation holiday, which would be stronger evidence if he wasn't already terrified he'd altered time.
And the TOS theme does have lyrics, though they're terrible and Roddenberry just wrote them to unapologetically steal half of Courage's royalties.
Ilia's theme from TMP also had lyrics.
I've always thought the Romulans weren't just the Vulcans who rejected Surak's teachings, but also any who didn't have the physical ability to follow them.
Originally it was just based on Romulans not expressing any psychic abilities, but Picard also established that sharing personal details publicly as a major taboo. That would track with them being a mix of former enemies who are concerned with suppressing the rivalries that lead to nuclear war.
"Spock's Brain" actually was licensed and performed by a community theater as a comedy. The teaser and part of the first act used to be on YouTube.
She played the captain of the Lakota later in DS9, Captain Benteen.