Interesting; I too wear injinji's out pretty (too) fast, but for me it's always the ball of the foot that wears out.

Great for toe blisters, but an alternative is a light silicone separator that keeps the offending toes apart. These are available from a variety of places; footsmart.com has a pretty good selection of such foot related stuff, but if I recall correctly you probably want to give a "expect periodic spam here" email address to them, plus expect some occasional snail-mail spam as well if you ever purchase.

As long as I'm rambling, someone mentioned always using gaiters. So many different approaches to backpacking! I rarely wear gaiters as my pants are long enough that little gets into the shoes. With no gaiters I think my feet are just that much cooler and the shoes can dry out faster when wet. And since the shoes are easier to take off and put back on I'm more willing to take them off to air out my feet at even a short break. In general I just like having one less thing to fiddle with.

There's no single "right answer" here, just an interesting collision of differing experiences and conclusions.