SMD was good science fiction, and it was even fair ST. Especially for its day. S:M was good science fiction, but lousy ST, because it involved, in effect, techno-telepathy at a distance. Both were lousy in terms of continuity, but then again, that was typical of that era, when the very idea of ST returning in any form other than prose was beyond most people's wildest dreams.
Even today, continuity is really only of concern to geeks like us, except in special cases like soap operas, or miniseries, or in JMS's 5-year miniseries, Babylon 5. And of course, there are series that deliberately thumb their noses at continuity, regularly killing off characters only to have them reappear unharmed the very next week (my understanding is that South Park does so, although I've never actually seen it, and that The Simpsons also does so, although I'm not sure I've seen even a single episode all the way through).
BTW, as far as television series being resurrected, yes, it did happen, but not, so far as I'm aware, with anything that only ran three seasons. Dragnet was resurrected (fairly successfully, with Jack Webb reprising his starring role) in 1967, and Perry Mason was resurrected (failing at 15 episodes, without so much as a single member of the original cast) in 1973 (it, of course, returned as a series of 30 made-for-TV movies starring Raymond Burr, in 1989).