Finding the right shoe as my needs change

Question
I've been Nordic walking up and down the hills around my home for several years now.  I wear Spira Classic Walking shoes, which are relatively heavy, with a great deal of shock absorption and not much drop from heel to toe.  I like them.  Over the past few months, I've participated in a more rigorous exercise program for weight loss that includes running.  I've also increased the pace of my Nordic walking, sometimes even running a bit.  During this program I've heard a lot about "running flats," and how running shoes differ from walking shoes.  What's piqued my curiosity the most are the new so-called "natural" or "minimal" footwear, including Vibram FiveFingers (with a pocket for each toe and very little padding), and minimal shoes by New Balance, Nike and other manufacturers.  

What's your opinion on such minimal footwear, especially the FiveFingers?  I'm told they allow your foot to build up muscle so that you can run more naturally, with less chance of injury, even though there is much less shock absorption.  I even met a doctor who just ran a marathon in them.  If the FiveFingers is going too far in design, what about trying a more conventional minimal shoe instead of the relatively massive and heavy Spiras I've been wearing?  And which type of shoe is best for the combination running/walking I'm now doing?  

It's a big decision, not only because my foot health is involved, but because all of these shoes are expensive, so it's hard to simply try out several different types.

Any help would be appreciated by this fellow "Expert" (Screenwriting).  Thanks.

Answer
I have no experience with the minimal shoes you mention. I have done some barefoot running on soft grass a few times to see if it would strengthen my feet. I noticed no benefit but probably did not do enough to have a real effect. The theory makes sense, but I fear most people's foot mechanics may be poor enough to get them injured before the minimal shoes can strengthen their feet.

If you have avoided injury with the shoes you are wearing (I am not familiar with them#, perhaps your mechanics are pretty good to start with, and you could benefit from trying them. If you do, be sure to use them for short periods at first, then gradually increase the time.

I am a pronator, but have used about every kind of conventional shoe out there. I passed the 100,000 mile mark #running and walking# last December, have run over 50 marathons, 111 ultramarathons and countless shorter races. In 36 years, I have had two significant running injuries #lower back and groin), both from slips. There have been a few minor overuse injuries along the way, but nothing major. I'm pointing all this out to emphasize that conventional running shoes have worked extremely well for me for a very long time in lots of environments and multi- hundred mile races.

If I had used the minimal shoes and strengthened my feet to eliminate my pronation, I might have been better. But I don't see how.