Trying to grasp the AD for wing spars

[YankeeClipper]

I've read quite a bit about the 78-09-05 AD but am still lost on a few things.

1) Mandatory or not for non-commerical, private owners and operators?

2) Why wouldn't someone want to inspect & repair even if not?

3) What are the ball park costs associated with a) inspection and b) remediation? I read figures up to $60k.

Thanks.