Yes, those areas did at one time match the glow of the hull (the topsides). I've done the procedures described in the link you received on the topsides of a couple boats, and with outstanding results.
Last season, I tackled the deck and cockpit areas (where there's no non-skid). It's a fair amount of work and hassle, because of all the stuff that's attached to the deck, and you have to work around it. For the most part, a 9" wool compounding pad on a grinder/polisher is like putting in tacks with a sledge hammer. When that big disk is spinning at 1200 rpm and snags on a chainplate, it's annoying to say the least.
If you're motivated, though, it's a job that you can do, and if done right, will last a long time if you keep it waxed.
MaineSail (who provided the info in the link) will take you through the necessary steps, which boil down to using the right tools, the right abrasives (wet sand and compounds), and the right pads. Veer from the path, and your results will be diminished.
So, read what MaineSail has to say. He doesn't say much about doing decks, but what he says about doing topsides transfers to decks. It's all gelcoat, after all.
On my decks, I started with compounding, followed by a finer compound. I used 4" disks, and it was still tricky. In some places I resorted to doing it by hand. Came out real nice, and got topped off with a couple coats of Collinite Fleet Wax (per MaineSail).
My boat's a 28 Catalina, and I didn't attempt to do the entire thing at once. I kept a log of my progress, and did half the cockpit at a time, one side of the cabin at a time, etc., until the entire thing gleamed. I get more compliments than I expected. If that matters.
I probably should have wet sanded prior to compounding, but that can be a tough call sometimes. It all depends on the current condition of your gelcoat. I probably could have started with 800 grit, 1000 grit, and then compounded from there. Oh, well.
From what you describe, you probably want (assuming you go through with this) to start with 800 and proceed from there. You don't use a rigid sanding block. Use a sponge, and wrap the sandpaper around it. And yes, use it wet.
How much work is it? It's a whole lot more than waxing your car. A LOT more. Still, it's hardly the worst job you'll tackle on a boat. You will need to read MaineSails instructions a few times, and continue to refer to them, and do a little study to be sure you have the right products and tools. Once you've mastered it though, it's like having a super-power. You'll be Shiny-Gelcoat-Man.
Someone will likely respond to your post and suggest using Poli-Glow instead of compounding. Less work, and not as good a result IMHO.
Oh, and if you give compounding a try, take very special care when using a powerful grinder/polisher in some of the cramped quarters in your cockpit, as it's EASY to get your extension cord caught up in the spinning grinder. Get a finger or thumb caught up in it, and you will be very sorry. Seriously. I got my thumb caught once when doing the topsides...don't let that happen to you.
