Why send a 160 year-old Ambassador on a mission deep into enemy territory, with enough Red Matter to rearrange the universe when only a single drop is enough to collapse the supernova?
Maybe because Spock had been living on Romulus since at least 2368, and is trusted by the Romulan people?. . . maybe because he is the one who promised to do it?. . . and Vulcans live to be over 200. . .160 is not THAT old. . .
~FS
You forgot to address the second part of the question.![]()
Because Red matter is more stable in large quantities. . .why do you think so much care was shown when extracting a single drop of it? Plus. . .it takes an extreme amount of heat to ignite it. . .a supernova, the core of a planet, a matter-antimatter explosion. . . it's containment field seemed safe enough. . .

~FS