Re: Cal 28 Vs. Catalina 27 livaboard
Backing plates - hard to tell from the photo but those look like stanchion backing plates, given the layout of the bolts. I've seen other owners do the same, but with solid wood rather than ply. If you wanted to change the backing plates for the shrouds, you could do it without taking the mast down.
2) You found moisture in the anchor locker? I think this is probably fairly common.
3) I'm disinclined to comment on the through hulls. I'm guessing that they're bronze, not brass, which does turn green. I think it's okay.
4) The manual probably says to change the impeller every year anyway, but it's possible it's something else. When you say "does not pump water" do you mean that the motor doesn't "pee" or that the pump doesn't move water at all?
Price - look for similar boats in your area on Yachtworld. It's very area-dependent. But assuming the conditions in the photos generalize somewhat to the rest of the boat (not in terrible condition but far from perfect) you're probably looking at $5 - $10K.
1972 Catalina 27