Maybe it's my nostalgia talking, but I feel that older Trek treated characters more fairly and let them have complete storylines, so even if they were written off, their stories felt more complete and almost satisfying, even if they got a sad ending (like Dax, for example).

I really don't think it's just your nostalgia. I feel the same way.

And you're right--probably with teh current showrunners, longer seasons wouldn't make me happy. But I miss 90s Trek a lot!