I don't think there's a certain answer. Aluminum alloys especially vary in their reaction to salt air. Many will develop a white oxide coat (which stays soft and continues to wear) in just a few weeks of salt air. Others are unaffected. Who knows which ones you have?
But then again some makers, particularly "Westerbleak", paint everything in sight including all the rubber parts and fittings which the rubber companies say should never be painted. Because it looks pretty and is easier than masking, I suppose.
Since you've got them all clean...shine 'em up, apply some wax or polish or other product, and see how it goes after a week, a month, six months. If they stay looking acceptable, by all means leave them that way. If they start to get ugly or show white powdery residue, it will be time to prime them (aluminum needs special primers) and paint them.
But of course any "iron" parts will rust, if there's no oil film, no paint, no nothing to protect them. Or at least, form a light coating of rust. Even on a car, the bolts under the engine compartment are protected well enough by an oil film, but they'll bloom with rust within a few days if they've been steam cleaned and the film knocked off.
Things like the exhaust manifold require special high-temperature paint, and usually you have to run the engine so it heats up and bakes on after being applied. Makes a bit of a stink while doing that, too.
Last edited by hellosailor; 03-17-2011 at 10:33 AM.