In reply to climb the peak:
Feet are as flat as pancakes. I have othortic insoles from Boots, only problem I find with them is I too sometimes get that middle-of-arch blister (got HUGE ones after a 10k race...nothing after a 50 km ultra) but I've inherited my mum's feet, and the 40-odd years she went without insoles has left her feet completely broken up and she now quite often has problems getting shoes to fit (narrow heel and very wide across the toes, plus the joint at the base of each big toe sticks out so making a lovely pressure point). I'd rather take the blister!
When I got a new pair of trail shoes, the guy in the shop said it's not such a problem when running over rough surfaces as you're not repeatedly loading the same stresses as you would on a flat surface, where your foot always hits the ground in the same way.
I would NOT say it's a case of "if it's not broken, don't fix it" as the breakage will happen further along the line! My mum (who has always done a lot of walking) was facing an operation 10 years or so ago, until she went to see a specialist who recommended insoles. The moment she put them in her shoes she could feel the difference- the pain from her broken up feet went.
I see it as prevention- I'm only 24, but I know I have her feet and I will try whatever I can to avoid ending up quite as bad as hers!