Inattentional Blindness

Inattentional blindness is a topic that we discussed previously in chapter four, sensation and perception. However, we didn't talk too much about it, and I found it rather interesting. By definition inattentional blindness is our failure to detect stimuli that are in plain sight simply because our attention and focus is elsewhere. Meaning we're looking but not really looking.
A few experiments were done in particular that fascinated me. In our discussions we watched a video where a man stopped random people on the street and asked for directions. However mid-way through he switched places with someone else and the other person never noticed. They did this experiment with different races, age and even gender. While watching it I couldn't believe that these people couldn't notice the change in a person, it seemed so obvious. So I became more curious whether I would be able to detect something so obvious.
In one of my other classes we looked at several pictures that would flash and something would change every time. Surprisingly I could only detect the change in one of the photos, so evidently I can't detect the obvious. While reading up some more about this crazy blip in our perception, it was said that humans are actually really poor at detecting stimuli even in our plain sight because we focus too much on one area. To me this seems like a dangerous thing because how many times is danger headed our way, but because we aren't looking for it we are missing it completely.
The thought of inattentional blindness and also change blindness makes me curious if there is any way psychologists can test an individual's blindness. Also, are there varying degrees of this blindness? Do we ever have hope in the future that with some psychotherapy, we can improve ourselves to be less "blind"?
Links:
http://youtu.be/vJG698U2Mvo
http://youtu.be/b7LuvAM6XLg