You've heard all the answers, here's mine. The mirror polish will dull in about a month. Every 2 weeks or so, you can wipe them with Mothers or SemiChrome, just a little more than you would wipe the painted parts at a routine wash down, and get 85 to 90% back. You can leave it for a full summer and lose 40%. At that point you'll never get back to mirror with hand polish. But you'll get back to 80%.
IMO you'll never get back to the original degraded finish, unless you leave them un touched for roughly the same amount of time.
Assuming you loved it enough to polish or have them polished, you'll love it enough to wipe it occasionally and keep it fresh looking. Wipe them after a wash to remove water spots. Polish when you can.
I wouldn't put anything on them except polish. No clear.
I'm assuming you actually ride the thing in all kinds of weather, wash/and wipe it down occasionally. If you're babying it, better results.