In fact, if it weren't for the tear in the upper, they would probably last me a good deal longer. I believe that as you get older you become more and more "asymmetrical" as you collect little injuries here and there that cause subtle changes to the kinetic chain that are not the same on both sides. In fact, we are born slightly asymmetrical to begin with (and no, I wasn't thinking about that). Perhaps if I improved my running technique I wouldn't wear out the shoes in this way but I think I have gone far enough down that road and, if my body has decided that my left foot should land in that particular way, I'm sure it has a good reason for doing so.
I thought I would try something different. Soft Star have started to offer a version of their shoes (moccasins really) with a "tough leather sole". They make it very clear with several disclaimers that the leather soles have much less traction than the rubber Vibram soles and so should be worn with caution, but this is something that doesn't tend to worry me unless I am running in mud or in hectic places like Vietnam, or indeed in mud in Vietnam. The sole is about the same thickness as the Vibram sole (5mm) and has a veiny patina which I guess will make them slightly less slippy than a new pair of dress shoes.
The leather sole is both softer and much more flexible than its Vibram counterpart. This is both a good and a bad thing as it's not really possible to have one without the other. Flexibility is good but the worry I have is how much it will hurt if I land on a stone while I am running. I did some unscientific tests at home involving wearing a Vibram sole on my right foot and a leather sole on my left foot and jumping onto stones and couldn't discern a difference between the two. It's kind of annoying when you land on a stone but it's not really all that painful. The other question is how much more durable (if at all) the tough leather sole will be... These two doubts will be answered over the next few months as I put them through their paces.