Is saving $100 worth ANY risk?
I'm a FF/EMT with 20+ years in the field and have seen some M/C fatalities and TBI's. Neither of these is a good thing!
I think it is stupid to argue about helmet replacement. JUST DO IT!
My thinking is this: if you replace your helmet every five years (even if based on "scanty" evidence), and it costs $500 for a new one (of course you can get a DOT/SNELL approved for much less $$), you are paying $100 a year to ride with a decent, clean, possibly state-of-the-art, allegedly safer, helmet. You likely spend more than $100 a year to buy other unnecessary items to wear or for the bike. Why would you NOT be willing to spend that on your head?
Experience is something you don't get until just after you need it.