The alternate time - yes, it does open up a whole new door. It seems like there was a TNG movie where they did something similar, but I can't remember which one or how exactly it worked. It's a grand concept, but one I have difficulty wrapping my head around until I've seen the film enough times.

At first I thought the guy in the cave was Spock's father - I was thinking, "Oh, maybe (young) Spock dropped Kirk on this planet on purpose" - though why he'd also send his father there I wasn't clear or what he was intending they'd accomplish.

But then he turned around.

Gotta admit I didn't pay a whole lot of attention to the soundtrack, which is probably saying a lot in its favour - because if the music is bad or jarring, I generally notice that.