Sure, The Feds aren't cavemen in TOS times, but, they are a good 100 years behind Spock's technical know-how, so, if Spock were to try and shape the Galaxy in his image, by spitting ot everything and getting them 100 years further in technology in a matter of a couple of a years, it could be very catastrophic. Pointing out the Prime Directive, wasn't meant to say Spcok would be breaking rules/laws, but, there is a reason you let Civlizations drive their own course, and that's because giving knowledge/technology that wasn't earned and properly understood (And the gravity of that knoledge appreciated) can have disastrous outcomes
I do agree, he should share some stuff sparingly, to avoid some of the worst stuff from happening, but, it should definitely be sparingly and with proper weighing, because the more he decides to "guide" them into the future quicker, the more likely he will make a bad choice that leads to a disastrous outcome.
I don't think the writers need to kill hm off to prevent the "Spoilers for the Future". I, in fact, think they should use him to impart some information for a nobel/good cause (As in saving Edith Keeler) and have it lead to unexpected dire consequences