I read and reviewed over 300 scripts on a now-defunct peer-review site. I only read one that I thought would make a good movie (and it would have had a niche market).

Maybe 10-20% of the scripts had none of the flaws in your bullet list. (My own scripts had quite a few.) They were well-written scripts as far as technique went. They were quite successful as a read. But in my opinion they would not have made a movie as enthralling as "Porky's 2."

What seems good in your head does not necessarily play out well in real movie time, even though a film of a not-very-good script may have a number of assets to bolster the audience's involvement (acting, music, cinematography, etc.). This I think is why in some cases a bad movie gets made or languishes in development hell--it seemed fine on the page. It may be what William Goldman meant when he said "No one knows anything."

But I think it's possible to train your intuition so that you have a pretty good idea if a script that reads well would make a good film. Most reviewers on that peer site didn't (in my opinion) understand the difference between a script and a film story. They'd often say something like "I'd love to see this" or "This script is so much better than most movies that get made today."

You simply can't compare a spec script with a filmed script. They are different animals, even if you ignore the acting, music, etc. of the film.

To answer the original question: I think the must useful bad scripts to read are the ones that are almost good enough to be good movies. That's the most significant barrier we writers have to overcome.