To summarize, the only thing Spock said that we should disregard is that there's 10,000 Vulcans left.
If it's the only implausible thing, sure.
alone, even at a Bronze Age level of development, would support a population of tens of millions of Vulcans. Romulus, a world settled by Vulcans who've developed an expansionistic culture defined by Vulcan models will understand on the homeworld, supports a population of billions of Vulcans. What we know about the Rigelians suggests they're Vulcan-like enough that drugs used to stimulate blood production in that population work well enough on Vulcans.
The existence of these three large populations alone, well-established in canon, demonstrates that Spock's initial assertion is incorrect. His is not an endangered species.
Add to this the implausibility that a well-established interstellar civilization wouldn't have a large population away from its homeworld, and the director's own statement that the "ten thousand" figure refers only to the number of Vulcans evacuated from the planet--not the total number of survivors--and, well.
Sure, Orci said that in passing. In future movies, he may well contradict this; he left himself enough room to do that. Until then, we've got a well-documented statement of canon that's backed up by other canonical information from the film and by novelverse canon.
Also, revenge upon a helpless enemy is a good and valid action.
Who said that? Young Spock did, sure, maybe a bit more than a day after the unprovoked destruction of his homeworld and its population and his mother in front of his eyes. As I said, it'd be a rare person in that situation who wouldn't act in that way.