Polished Engine Parts Care

I've been thinking of having my plenum, fuel rails, and lower plenum polished to a mirror shine. I was wondering what kind of care this will require once it is done.

Will the metal dull out and be ruined after a few weeks if I don't religiuosly care for it?

Ideally, I want it so I can leave the thing unattended for a while and clean it up when I wanted to and it would look as good as the day I polished it.

Is there some kind of "clear coat" that can be applied to polished metal for protection purposes?

i've had a polished spark plug cover for 8 months now, haven't done anything to it, still shines