In regards to my project boat (75 sunray 15'5) I'm wondering what others
think about wooden floors, and when to change them. From what I
understand
the floors of all these boats are built with marine plywood thus they can
take a beating being wet.

Methinks you will end up replacing the entire floor. This happened to me and
the rot had progressed all the way into the transom. Ugly, ugly, ugly.