To report: In the end I bought the Shurhold Dual Action Polisher Pro, for $250. 6.5 inch random orbit, 900 watt motor. Yeah, there is a Harbor Freight apparent equivalent for under $100. Does it vibrate, deafen you, and explode in three months? Who knows. There is so much conflicting information and advertising and car-shop guys with strong opinions that I finally just gave up being led in circles and ponied up for the Shurhold, which comes in a pretty red bag made by children far away.
My conclusions, after sifting 1,000 arguments, and ready for correction:
--Any real shine comes from the compounding stages, which I skipped because the boat was recently compounded.
--The polymer product used (Shurhold's Pro Polish) is easy to use and left a minor shine, about the same as my last $1200 professional job.
It is easier than wax simply because it leaves hardly any residue to be wiped away. One microfiber rag or bonnet for the whole deck.
I first washed the deck with boat soap, hand scrubbing away small amount of occasional mildew.
Polishing took total six hours, in two sessions. Not too bad, lots of bending of course. Deck only, not hull. The deck and transom take most of the UV, the topsides seem much less affected.
The intent is merely to preserve the gelcoat, and by all accounts I'll have to do this 2-3 times a year in our SoCal environment.
The real equipment required is to live near your boat and be retired.