D8 is wrong, well nearly so.
SIDS came about because a C402 landed in the US with the pilot complaining that he had run out of aileron trim to keep it level. The aircraft was high time (> 20,000 hrs from memory) and had been used on a short sector low-capacity RPT run (lots of pax & bag weight). On inspection the aircraft was found to have a cracked spar. It was well on its way to an in-flight break-up.
It was then that Cessna came to the decision that their aircraft were being used far more than the original design envisaged and that if they were to be kept airworthy then something more than the run-of-the-mill inspections were required.
I have seen what SIDS have uncovered by way of unseen corrosion on C310 and C206 aircraft. I have also heard about what has been uncovered on C172 aircraft, a design that was believed would have very few problems. Yes, SIDS is expensive and no, it doesn't had the equivalent value to the aircraft, but if we wish to continue to operate ageing aircraft it would seem to be a responsible decision.