The TNG timeskip is a clever one because it came bundled with "and we are not mentioning X, Y, or Z, this is about NEW STUFF" in the bible that mostly held for several years - forcing writers to actually do new stuff instead of "hey, remember the Gorn?" (This may, as Lance Parkin's argued, partly be Roddenberry trying to severe the concept of Star Trek from Nimoy, Spock, and the Vulcans, which was the best thing for Trek's longetivity even if it was because the two men didn't like each other)