Center boards require very little extra maintenance. The well and board need to be cleaned and painted when you do the bottom but that's minimal time and labor. The cable should be inspected at each haul out and replaced if necessary. The galvanized cable that the PO installed on my boat still looked good after 6 years mostly in Hawaii. Changed it out for a Dyneema line which is going on 7 years and possibly will last forever. The plumbing to run the control line needs to be monitored but my boat is 50 years old with everything but the cable is original.
I've got a Pearson 35 but most center board installations are essentially identical. How the lifting cable is actuated and located is the big difference. Different boats's interior and deck designs so builders have routed the lifting cables differently with different means to multiply force to raise the board. Some use a wire reel or sheet winch mounted either on deck or below. Others have a simple dual sheave arrangement to multiply force. I'm not familiar with any center board mechanics that lock the board down on a keel/centerboard boat. There may be some out there but I'd be leery of such a set up unless it is built hell for stout to be as strong as fixed keel. Personally want the board to lift up and save itself when it hits the bottom. So most boats just rely on the weight of the board to keep it lowered all the way at sea. Some may have minor weight ballast to be sure it stays down but in no way is it enough ballast that would affect stability. There are boats with ballasted lifting keels, either swing or vertical, but they are a whole different barrel of fish.
The board in the up position should have little to no bumping, banging. Sailed to Hawaii DDW with the board up with the rolling that that point of sail includes and the board was dead silent. The only time I was aware that the board was even there was when the lifting line slipped a little in the cam cleat and the board dropped down a bit. Hauled a bit on the lifting line and was back to silent running. Lowered, the board can bang. Beating, it seldom makes any noise. On a reach or run it does make itself known because of the additional rolling of the boat. But then I almost never lower the board except when hard on the wind because it's not necessary and just makes for additional drag. Some people say partially lowering the board on some points of sail can affect helm balance but haven't found that to be the case with my boat. Lowering the board at anchor with ANY wave action will result in the board bumping noticeably. Don't know why you'd want to lower the board at anchor in any case.
Wow, I have to disagree with just about all your impressions of a centerboard, but of course, we don't sail similar boats.
I've tested it time and time again under power, and there seems to be zero drag; we don't even lose a .10th of a knot with it down. As above, we almost always use it at various depths to balance the boat and slow the roll, even ddw. That yours causes you to roll more on a reach is unfathomable to me, as putting ours down has an amazing effect to dampen the roll. We can always tell if we have forgotten to put the board down because she rolls so much more, even at anchor. At anchor, on our boat, there is a sweet spot where it dampens the roll and doesn't bang.
I know of folks who have put garden hose cut in half lengthwise on the board above the part of the board that comes out of the boat, and others who have used a similar method at the opening and it has completely stopped the banging.
Of course, when one can increase their draft from 6' to over 10, that has a considerable effect on leeway when beating. But when we are sailing well, the current seems to have little added effect.