On the topic of intentionally making your bike ugly to theft proof it, that reminds me of when I was in college. One of my TAs had a nice new white bike but there was some black spray paint around the headtube lug work. I asked him if there was a problem with his frame, he said no but that he had already had two bikes stolen in the past year so he was going to make this one more ugly.

Another college friend had a really ugly rusty single speed bike. I think it had 24 inch wheels, was bigger than a small kids bike but smaller than full size. He rode it everywhere for over a year, did not ever lock it. And on campus to not lock up a bike for over a year without theft was virtually unbelievable. Finally he blew out a tire and had to buy a new tire for it. Within a week someone stole it for the tire.

I live in a college town where bike theft is bad near campus, but the further you get from campus the safer your bike is. I rely on low cost cheap locks for my expensive bikes, but mostly ride far from campus. When I go near campus I am more inclined to ride my rusty errand bike that I paid $5 for at a garage sale than I am one of my good bikes. I put a lot of new parts and newer tires on it so it has some value, but the old steel handlebar does not have any paint on it any more, the rusty patina on it likely aids in theft prevention.