A shiny kettle is nice, but a clean kettle is essential to producing good beer. Soaking a kettle with beer stone in P.B.W. will loosen the beer stone or caramelization making it easy to wash off with hot water and little or no scrubbing. A stainless steel S.O.S. pad can be used for the stubborn spots. Never use a chlorine based cleaner or sanitizer on anything made of stainless steel. The chlorine can pit and corrode stainless steel.
Kettle valves are great places for harboring bacteria. To prevent infecting a batch, remove the kettle valve after brewing. Rinse it out thoroughly and clean it so sweet wort trapped in the pockets does not allowed bacteria to grow between uses. Then it's a good idea to boil it before each brew.
To prevent the black soot from forming on the bottom of the kettle during your boil, rub regular dish soap on the bottom of the kettle prior to placing it on the propane burner. The dish soap will turn black rather than the bottom of the kettle and it will rinse off. Clean kettles make happy brews.