Can't answer all your questions but we might be able to help with a few...
After years of shopping and looking at the 34+ vs the 37+ we made our decision, we bought the 37+!
How is performance with the centerboard vs. Wing?
We have no experience a centerboard but we can say that the wing keel version can still point like the other C&C's we have sailed. We were not at all disappointed with her performance, we are used to racing and she can out point the best of them.
How roomy/comfortable is the cockpit?
At first glance, what looks like short uncomfortable angles jn the cockpit compared to the 34+, is a misconception - we love the cockpit! So many areas to sit and chill, no mis-stepping here because all levels are designed perfectly. Companionway hatch/cockpit area is incredibly comfortable while cruising or racing
Is the companionway awkward?
Not really - the platform halfway down helps. Could be a problem for dogs entering cabin (stairs are long).
Is the aft cabin as nice as it looks in pictures?
Yes, yes, and yes! The ability to get up and not have to crawl out of the aft berth is huge!
Any specific maintenance issues other than the cited hull?
Chainplate/deck area is an area to watch on all decks. The hull is balsa cored, while ours has epoxy around all thru-hull fittings we had it surveyed with a flir camera to ensure the hull and deck was sound.
We loved the size of the 34+ (36'), but the 37+ (39'11") has so much more space, storage, etc.
Hope we helped. We love our 37+!