Memphis Belle? Flight of the Intruder? neither were cheap and both were really good IMHO. I think we (real world pilots I'm speaking to specifically) have just become a bunch of snobs when it comes to aviation movies, we complain that there aren't enough but when one does come along, we then complain if they are 100% realistic, unfortunately we cant have it both ways.
You are right, there have been some great films, but they are few and far between. As far as realism goes, Hollywood is about selling dreams and a bit of "enhancement", is often part of that. But how far it goes is up to the director and the producers.
That said, I can enjoy a movie based on nothing more than real planes flying through the air. One of my favorites "Strategic Air Command" is nothing more than a paper thin plot and glory shots of SAC bombers flying through the clouds, and I've watched that twice in a row on occasion.
Basically, the only aviation movies that disappoint me are the ones where the planes hardly leave the ground. In those cases, the plot and acting have to be first rate.