Lots of options here!
If the door is "wood" or Decraguard", and you like the wood look, the route that replaces the plastic laminate with another formica piece is the best, providing you have the tools and skills to cut, glue and edge it.
Refinishing a real wood door takes more judgment on how far down to sand the wood , how to re- stain it (if necessary), and what to use as a coating. I'd suggest clear POLYURETHANE as it is more durable than anything else (harder to chip, etc). (See below)
Another option would be to just sand and paint the door with a solid color, one that matches the trim color of the boat. I've seen this done, and it looks very nice and even original! Again, polyurethane is the toughest paint available, and a pigmented (colored) paint will last quite a bit longer than a clear one due to the increased resistance to UV light deterioration with the pigment in the paint. This principle works with all paints, basically. Epoxy would be good too, but polyurethane is much more flexible, chip resistant, and flows out better to a flatter finish with a higher gloss.
The best polyurethanes and epoxies come in two parts that react (really polymerize) together, but a single part paint that dries reacts in the presence of air would be fine on a door.
If you like the looks and don't mind the increased loss of privacy, one could also always go to the factory or a plastics supply outfit and have a clear door made up like the new boats. If I did that, I'd use a smoke tinted plastic to limit the view to the inside, etc. The big drawback would be the price, with several hundred dollars being the expected price tag. You'd probably also have to change the lock hardware, too, due to the difference in thickness of the door. Maybe the hinges would have to be reset somewhat or replaced too, due to the way the new door would fit into the doorway. Would have to think this one out carefully before committing to it!
Just a few cents of thoughts for free!
Joe. :teeth :thup