I saw Respect on Tues., 9/7. I thought the story was interesting, performances were good. That film was too long for me.
I didn't feel that In the Heights was too long, unless you are just referring to the post-credit sequence. It was cute, but certainly not necessary.
I'm pretty selective about films that I see. I do as much research as I can, check reviews, ask friends, then try to avoid films that don't interest me.
Films did not always have extensive credits at the end. I don't recall when that changed, probably some time in the 80's. Today's films have credits that go on for 5 to 10 minutes. However, most audiences leave when the credits begin.
Casablanca is one of the greatest films ever made, superb editing, not a wasted second, storytelling at its finest, but Curtiz was rarely ever that succinct. Many of his films were way too long -- Casablanca is one he got right.