Firstly, I would love to have a conversation with owner of the boat. That trim tab was obviously installed by a tuner (somebody who is always looking for improvements on a design, sometimes for a specific sailing condition).
Secondly, the twin headstays also allow headsail changes without going bare headed.
Thirdly, my Cal 25 had the same rudder issue. The 25s rudder has a foam core, and a very light glass mat/gelcoat skin. I removed all of the flaking skin, soaked the foam with penetrating epoxy, filled with micro balloons and faired the rudder to a proper NACA foil then re-skinned with 6oz fabric and epoxy. No problem, but I'm a bit of a tuner myself and enjoyed the project.