As the owner of a Hunter 54 I can answer your questions.Its in Newport Beach harbor on a mooring.
Yes the interior room is small for a 54-foot boat. The v-berth is plenty for two people but the rear stateroom berth is barely adequate.
Most of them come with either the original 36 hp (Perkins I think) which is a little underpowered or like mine 76 hp yanmar (more than enough)
Weak points are the plate that the keel bolt nuts go on top of; tends to corrode, and the steering quadrant. It is attached to plywood which tends to rot out and you lose steering at the wrong moment. Not hard or expensive to fix with carbon fiber or fiberglass reinforcement, just be aware.
The
dinghy garage is usefull but cannot fit a normal size
dinghy in it without letting the air out. Lots of writing out there on forums that this could cause problems in a following sea with it getting filled in, but have no experience with this. But the transom is really useful for boarding.
Got new mainsail and headsail in 2006 from UK sails, cost $10,000 for both including
lazy jack system and sail cover. In light winds it sails okay, but once you get 10 knots or above it really starts to move. PHRF rating is 51.
Under power you really need an
autopilot. The boat will "turn on a dime" but has no directional stability under power. But under sail I can trim it to be more or less hands off.
I have had no core or structural issues. The bulkheads are not attached to the hull and so in any motion its noisy. Definitely not a blue water boat, but fine for coastal.