I have had my metal from new since November & have become quite anal about washing it.
I normally wash it about every 2 weeks & I do it like this
meguiars snow foam shampoo with snow lance
Hand wash using meguiars shampoo with lambswool mitt & 2 bucket method
I have never dried it or polished it yet & it still shines like it has just come out of the show room
The alloys are a nightmare but it helps that mine are black lol