CobraRoll, you made reference to and inclosed train rollercoaster being a monorail, but have you ever seen rollercoaster travel at 60 mph going through loops, bunnyhops and other coaster elements? The sensation of the wind in your face is one that I think everyone enjoys, but do you think the feeling of air time or g-forces would be different?
The idea of the having inclosed cars and traveling extremely close to outside object would create a totally new element to the ride. The perception of coming "too close" to an object would increase the excitement of the ride. I don't know it this would replace the feeling of wind in your face, but I sure would not rule it out.