I have to be a bit less precise and say that I like an open ending and a closed ending as long as they suit whatever has preceded it. And at times I feel a film gives you an open ending to try and be smart and fails. The horror genre does this more I feel.
TWOK seems to indeed have an ending whereby if another film had never been made then you feel still a sense of resolution, whilst knowing their lives will go on. I suppose you can say the same for TSFS and TVH. And those endings are all fine. But I think that as Sam noted it's the difference between thematic sense and logical sense at times.
Star Trek is a lot of the time less about logical sense and more the former, because it's dealing with a 'family' and families don't always make sense!
Regarding Nemesis, as far as I always knew it was supposed to have been the last. But I still think they were intentionally leaving crumbs for another film (just in case). In that respect I would differ from Sam and have to imagine that 'if' Nemesis had made $100 million and then another TNG film had been made probably things like B4 would have been morphed into 'he's now settled with Data's memories and since he had no personality of his own before, he's essentially Data again'.
But we'll never really know.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist