Spock's line is meant to mean that there's 10,000 Vulcans (as opposed to Romulans) left altogether. Why else would he say he's a member of an endangered species? If China were destroyed would a surviving Chinese citizen claim to be a member of an endangered species if there were still 5 billion other humans left? Has there been any mention of Vulcan colonies that weren't in the TNG timeframe? P'Jemm wasn't a colony as much as a listening post. Maybe Vulcan didn't start colonizing planets until V'Ger showed them that one threat almost took out the entire Earth.
Nonsensical or not, the supernova is the way that Romulus will meet it's end. Seeing as Spock created the black hole after Romulus was destroyed I wonder what exactly he was trying to do? Clean up the mess? Create a fire break to protect another inhabited (Federation?) planet?