I carry a backpack just about everywhere I go. It always contains my laptop, various electronics, and some camera equipment. I have a tendency to leave things behind when I leave a place, so i try to keep it close at all times. I've been known to lose valuable items (such as expensive cell phones) in theaters by accident, never to see them again.
When I go to a movie, I take my bag with me. I'm not about to leave valuable electronics in the parking lot where they can easily be stolen. I am sure I have exhibited the same overprotection of my bag when I've just cashed a check and stashed several hundred dollars inside it. I do not let it out of my immediate control.
I agree with the sentiment of others, that if you were truly concerned for your safety, you should have left. In answer to your question, I don't know if you were being too paranoid. I wasn't there.
From my pedestrian understanding of your situation, I would say yes. I also drive an old vehicle, and many would consider it beat-up. I have had my car broken into and valuables stolen. Now, any valuables I have stay with me in my backpack, not the car. While it is prudent to avoid and report overtly suspicious activity to authorities, I think it is both unreasonable and contrary to the concept of free and open to society to make assumptions for the worst on what we imagine might be. I am certainly not willing to give up my up my right to privacy to obtain the "security" of protection from what might be. Such actions lead down a long and arduous path toward totalitarianism. Not to sound cliche, but Nazi Germany was a prime example of this in action. To quote Benjamin Franklin:
The fact that we as a society are becoming more and more willing to allow governmental entities to infringe upon our rights without probable cause or even a reasonable suspicion concerns me deeply. I do not want to live in a society where I can be searched and my property seized because of what someone thinks might be without any evidence to support that suspicion.Any society that would give up a little liberty to gain a little security will deserve neither and lose both.