I think two of the most important points you mentioned are what you called “take inventory” and “be prejudiced.” Not nearly enough people take this extra step in protecting their safety.
One thing implicit in your post that I’d like to add explicitly is that is that you should not only “profile” the passive signs that they may be up to no good (e.g., putting on make-up, busted car, etc.), but also actively try to figure out which drivers to avoid based on their active driving behavior. In other words, as you’re driving along, you should be tracking the cars around you for any irrational behavior (e.g., driving 20 in a 45 with heavy traffic with no signal on, sudden lane changes without signal or head checks, tailgating, any sign that a driver hasn’t noticed or isn’t likely to notice changes in conditions, etc.). This information should help you determine where to ride, and which drivers to get the hell away from.
To make an unwarranted analogy, it’s very easy to get injured in any sort of sport/exercise scenario, but with martial arts you have to be particularly careful. Getting punched unnecessarily hard by a sparring partner is one thing, but my weapon of choice, Brazillian Jiu Jitsu, revolves around moves that aim to dislocate, crack joints, and choke opponents. When I’m on the jiu jitsu mat, I go out of my way to profile all the other guys and try to figure out which ones are either a) too rough, or b) don’t have good “lock-sense” (i.e., don’t have a good sense of when their arm bar or choke starts to really kick in). Once I’ve identified these guys, I stay the hell away and, if asked to roll, politely decline. I learned this the hard way, after being put out of commission for weeks more than once by things like a torn rotator cuff muscle or cracked ribs.
Like IBA said, you should also be keeping track of every vehicle around you, especially ones you’ve identified as potentially hazardous. This is especially important when you have to take evasive action. If the car in front of you slams on its brakes and you KNOW for a fact that the left-most lane can’t have anybody in it, you can swerve away from trouble without hesitation. That extra two seconds to look and think about what you saw could cost you.