Oldbones,
I'm interested in what you say about the new Kayano's. I have been through about 8 pairs of the various models over the past couple of years, and been completely injury free. However, a few weeks ago I bought the latest version. They didn't feel any different, and like you I thought the only change was the colour. But over the past couple of weeks I have started to get slight pains in the arch of both feet (but particularly the right one) after running.
I was thinking that it couldn't be the new Kayano's, because they are exactly the same as the old. But since they are the only thing I have changed about my running, maybe they are the cause. Like you, perhaps I need (reluctantly) to think about changing to a different shoe.