For instance, before directing Wrath of Khan, Meyers watched every prior TOS episode, whereas Baird refused to watch any of TNG before directing Nemesis. The quality/lack of both films probably wasn't contingent on that, but ask anyone which film turned out better, and you'll get only one answer.
See, here's the thing. I agree that Wrath of Khan is by far the superior film. But I don't think that is in any way due to continuity.
The Gary 7 episode of TOS opens with the Enterprise orbitting Earth in in the 1960s because something something lightspeed time travel. There is, if we accept this episode as canonical, no reason why the crew of Star Trek cannot travel to any point in history at any moment, or why any FTL-capable species wouldn't be able to do the same.
Think of all the episodes where the crew of the Enterprise arrive at a location after some mysterious event and have to piece together what happened. Why didn't they just go back in time and see what happened directly? They wouldn't even need to change history, they'd just be observing events that from their perspective already happened, like they are doing in that particular episode..
Is that a better show? Is it a more fun show to watch because it has a harder continuity?
The reason Wrath of Khan works, and the reason it was probably important to actually watch the series before making it, is that Wrath of Khan understands the
characters and
themes of TOS Star Trek incredibly well and manages to heighten them to a cinematic intensity without compromising the emotional heart of the show. It doesn't matter, for example, that Khan talks about never forgetting Chekov's face despite the fact Chekov didn't appear in
Space Seed. That doesn't make the movie bad despite being a really obvious continuity error.
All the TNG movies have a pretty fundamental problem of not really understanding the characters, but Nemesis is one of the clearest examples. What should have come from researching the show is not an exhaustive knowledge of events in it, but an understanding of what the show's appeal is and what is important to people who would watch it. Wrath of Khan absolutely nails that, Nemesis does not.