> This is the number one thing I optimize for now: the ability to quickly and safely change significant parts of the code and product.

This was always a good thing. Its value has nothing to do with the advent of AI coding.

> The opportunity cost of not being able to safely restructure has gone up substantially.

This bit is contradictory with everything else you said. Prior to AI coding it would take a lot longer to perform restructures. If anything, the thing you're now optimising for has gone down in value. It's still valuable, but perhaps a little less.