My Weber gas grill: Over the years, I've replaced the deflector shields (those pieces that cover the burners) with stainless. The originals on mine were porcelain coated steel that eventually rotted away. The burners were already stainless. My grates are the porcelain coated cast iron, but over the years most of the porcelain coating has been worn away from wire-brush cleaning. I did have to replace the ignitor once. I've gotten over 15 years out of it, and have no reason to expect less than another 15 years. Mine sits on a covered deck, but I don't put a grill cover on it. Once a year, in the spring, I take it all apart and clean out the burners with a toothbrush and make sure there are no spider webs clogging up the air intake screens at the knobs. And I swap out the foil drip pan once a year now that the possum that used to clean it out for me finally got hit by a car.
I do need to replace the regulator soon, though.