I would suspect there's no real correlation, and what you've experienced is the luck of the draw. I bought out an old professional photographer once, and most of his stuff fell into the "beater" category. He did take good care of his stuff, but he used them a lot. As a result, some of it looked bad, but was in good shape, and a lot of it looked bad and was worn out beyond what reasonable repair costs could cover. I kept the good stuff, sold the bad stuff for parts and any of the good stuff I didn't need. I got it all for a good price, so I still made a good bit of money on the deal. But it taught me that just because something was well loved and used often, doesn't mean that it was in good shape.
I also have bought a few cameras from the late 80's and early 90's that were hardly ever used, and didn't work or only worked for a short while. They looked mint and often came in the original packaging, but the inactivity wasn't good for them. All in all, I think the best used gear is gear that is lightly used and carefully maintained over it's lifetime. That stuff is hard to come by, because those people usually aren't selling. The next best gear is gear that is easy to repair. As with anything, luck plays a major role. That's why "try before you buy" is so important.